U.S. patent application number 12/307613 was filed with the patent office on 2010-10-21 for process for making a healthy snack food.
This patent application is currently assigned to FRITO-LAY TRADING COMPANY, GMBH. Invention is credited to John Richard Bows, Colin Jeffrey Burnham, Jonathan Paul Coker, David Ellis, David Lester Hickie, Greg Paul Hilliard, Michelle Louise Lock, Norman John Maloney, Brian Richard Newberry, Rocco Dominic Papalia, Paul Frederick Tomlinson, Stanley Joseph Whitehair, Martin Yonnone.
Application Number | 20100266734 12/307613 |
Document ID | / |
Family ID | 38957601 |
Filed Date | 2010-10-21 |
United States Patent
Application |
20100266734 |
Kind Code |
A1 |
Bows; John Richard ; et
al. |
October 21, 2010 |
PROCESS FOR MAKING A HEALTHY SNACK FOOD
Abstract
The present invention is directed towards a method for making a
healthy snack food having an appearance and taste similar to
conventional fried snack products without the use of an oil-frying
process. The method of the present invention includes the steps of
providing food slices from a starch-based food or dough. The food
slices can be blanched and a controlled amount of oil can be added
to enhance final organoleptical properties. The food slices are
then rapidly dehydrated to a much lower moisture content in a
primary drying step that simulates conventional frying dehydration
rates. A food snack, such as a corn or potato-based snack, produced
by this method is a low-fat, ready-to-eat snack having the
conventional texture and taste associated with fried snack
products.
Inventors: |
Bows; John Richard;
(Leicestershire, GB) ; Burnham; Colin Jeffrey;
(Castle Donnington, GB) ; Coker; Jonathan Paul; (
Warks, GB) ; Ellis; David; (Flintshire, GB) ;
Hickie; David Lester; (Leichestershi, GB) ; Hilliard;
Greg Paul; (Coventry, GB) ; Lock; Michelle
Louise; (Sulffolk, GB) ; Maloney; Norman John;
(Buckley, GB) ; Newberry; Brian Richard;
(Leicestershire, GB) ; Papalia; Rocco Dominic;
(Plano, TX) ; Tomlinson; Paul Frederick;
(Leicestershire, GB) ; Whitehair; Stanley Joseph;
(Peekskill, NY) ; Yonnone; Martin; (Fairfield,
CT) |
Correspondence
Address: |
CARSTENS & CAHOON, LLP
13760 NOEL ROAD, SUITE 900
DALLAS
TX
75240
US
|
Assignee: |
FRITO-LAY TRADING COMPANY,
GMBH
Bern
CH
|
Family ID: |
38957601 |
Appl. No.: |
12/307613 |
Filed: |
July 18, 2007 |
PCT Filed: |
July 18, 2007 |
PCT NO: |
PCT/US07/73820 |
371 Date: |
November 5, 2009 |
Current U.S.
Class: |
426/233 ;
426/243; 426/302; 426/438; 426/465; 426/509; 426/523; 426/549;
426/615; 73/73; 99/451 |
Current CPC
Class: |
A23L 5/15 20160801; A23L
7/117 20160801; A23L 19/09 20160801; A23L 19/18 20160801 |
Class at
Publication: |
426/233 ;
426/523; 426/243; 426/509; 426/302; 426/438; 426/549; 426/465;
426/615; 73/73; 99/451 |
International
Class: |
A23L 1/217 20060101
A23L001/217; A23L 1/01 20060101 A23L001/01; A23L 1/307 20060101
A23L001/307; A23L 1/48 20060101 A23L001/48; A23B 7/01 20060101
A23B007/01; G01N 5/02 20060101 G01N005/02; A23L 3/01 20060101
A23L003/01 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 19, 2006 |
US |
11458592 |
Mar 14, 2007 |
US |
11686027 |
Claims
1. A method for cooking in a non-oil medium a food product, wherein
the end product mimics the organoleptic characteristics of a
fry-cooked product, said method comprising the steps of: a)
determining a dehydration profile corresponding to a desired end
product; b) preparing a food product for cooking; c) cooking in a
non-oil medium the food product at a controlled rate, wherein said
controlled rate is adjusted to mimic the dehydration profile of
step a) for the food product of step b).
2. The method of claim 1 wherein the cooking of step b) comprises
microwave cooking.
3. (canceled)
4. The method of claim 1 wherein the food product of step b)
comprises a food material selected from the group consisting of
potato, yam, beet, carrots, parsnip, sweet potato, turnip, squash,
courgette, asparagus, mushroom, broccoli, cauliflower, sweet
pepper, chili pepper, peas, sweetcorn, celeriac, tomato, olives,
aubergine, beetroot, fennel, onions, spinach, chard, cabbage,
almonds, peanuts, walnuts, pecans, brazils, pumpkin, sunflower,
sesame, poppy, squash, peas, chickpeas, lentils, pinto beans,
kidney beans, broad beans, butter beans, soy beans, runner beans,
black eye beans, oats, wheat, sorghum, rice, millet, rye, barley,
basil, bay leaves, coriander, mint, cumin, garlic, lemongrass,
oregano, paprika, turmeric, parsley, pepper, and mixtures
thereof.
5. The method of claim 1 wherein the fry-cooked product comprises
dough prior to frying.
6. The method of claim 5 wherein said dough comprises potato or
corn.
7. The method of claim 6 wherein said food product of step b)
consists of a dough, wherein said dough comprises 85% potato and
12% legumes by wet dough mix weight.
8. The method of claim 6 wherein said food product of step b)
consists of a dough, wherein said dough comprises 49% potato and
40% lentils by wet dough mix weight.
9. The method of claim 6 wherein said food product of step b)
consists of a dough, wherein said dough comprises 70% potato and
25% mixed root vegetable by wet dough mix weight.
10. The method of claim 6 wherein said food product of step b)
consists of a dough, wherein said dough comprises 70% potato and
25% cauliflower by wet dough mix weight.
11. (canceled)
12. The method of claim 1 wherein step b) comprises a blanching
step, wherein said blanching step comprises a wet blanch, or dry
blanch, or oil blanch.
13. (canceled)
14. The method of claim 12 wherein said wet blanch comprises a
medium comprising water at about 60.degree. C. to about 100.degree.
C., and further wherein said blanching step occurs for between
about 50 seconds and about 3 minutes.
15. (canceled)
16. (canceled)
17. (canceled)
18. The method of claim 12 wherein said dry blanch step is about 30
to about 90 seconds in duration and wherein said food product is
brought to a temperature of about 90.degree. C. to about
120.degree. C. during said blanch.
19. The method of claim 12 wherein step b) further comprises an oil
addition step after the blanching step.
20. The method of claim 19 wherein the oil is conditioned prior to
use in step b), thereby increasing the fried characteristics
provided by the added oil.
21. (canceled)
22. The method of claim 12 wherein said blanch step comprises a
warm oil dip of about 60 to about 120 seconds in duration and
wherein said food product is brought to a temperature of about
60.degree. C. to about 99.degree. C. during said blanch.
23. The method of claim 12 wherein said blanch step comprises a
flash fry for about 7 seconds to about 20 seconds in oil having a
temperature of about 120.degree. C. to about 180.degree. C., and
preferably for about 15 seconds to about 20 seconds in oil having a
temperature of about 150.degree. C. to about 160.degree. C.
24. (canceled)
25. The method of claim 12 wherein step b) further comprises a
de-oiling step after the oil blanching step.
26. The method of claim 25 wherein the food product is cooled prior
to or following the de-oiling step.
27. The method of claim 25 wherein the food product is pre-dried
following the de-oiling step.
28. The method of claim 27 wherein said pre-drying occurs in a
microwave pre-dryer.
29. The method of claim 27 wherein said pre-drying takes from 5
seconds to 90 seconds, and preferably from 10 seconds to 20
seconds.
30. (canceled)
31. The method of claim 27 wherein at least one quarter of the
water content of the food product is removed during pre-drying.
32. (canceled)
33. (canceled)
34. (canceled)
35. The method of claim 1 wherein step b) comprises adding natural
ingredients to said food product.
36. The method of claim 2 wherein the controlled rate of step c)
comprises a first microwave power step and a second microwave power
step.
37. The method of claim 1 wherein the controlled rate of step c)
corresponds to moisture removal between starch transition
points.
38. The method of Claim I wherein the dehydration profile is
determined by measuring the moisture level in a fry-cooked product
at a plurality of points during the time that the fryer-cooked
product is fried or an iterative process, wherein said iterative
process produces the desired end product.
39. (canceled)
40. The method of claim 1 wherein said controlled cooking rate of
step c) comprises a first dehydration rate of between about 0.02
grams of moisture per gram of solid per second and about 0.2 grams
of moisture per gram of solid per second, and wherein further said
controlled cooking rate of step c) comprises a second dehydration
rate of between about 0.004 grams of moisture per gram of solid per
second and about 0.08 grams of moisture per gram of solid per
second.
41. The method of claim 1 wherein said food product of step b)
consists of a dough and wherein further said controlled cooking
rate of step c) comprises a first dehydration rate of between about
0.04 grams of moisture per gram of solid per second and about 0.2
grams of moisture per gram of solid per second, and wherein further
said controlled cooking rate of step c) comprises a second
dehydration rate of between about 0.01 grams of moisture per gram
of solid per second and about 0.08 grams of moisture per gram of
solid per second.
42. The method of claim 1 wherein said food product is par-dried to
a half-product, and wherein further said half-product is packaged
for later finish drying by a consumer of said product.
43. The method of claim 42 wherein said food product is par-dried
to below its starch melting point.
44. The method of claim 42 wherein said food product is par-dried
to below its glass transition point.
45. A food product made by the method of claim 1.
46. A method for preparing shelf-stable food slices comprising the
steps of: a) blanching a plurality of food slices; and b)
explosively dehydrating said food slices to a moisture content of
less than about 20% with a microwave, wherein further said
dehydration comprises a first dehydration rate and a second
dehydration rate.
47. The method of claim 46 wherein the dehydrating at step b)
comprises a par-dry to a half-product, and wherein further said
half-product is packaged for later finish drying by a consumer of
said product.
48. The method of claim 46 wherein the dehydrating of step b)
occurs in a belt microwave with evenly presented, substantially
monolayered food slices or in a deep bed dryer.
49. (canceled)
50. (canceled)
51. The method of claim 46 wherein said explosive dehydration at
step b) comprises a first dehydration rate of between about 0.02
grams of moisture per gram of solid per second and about 0.20 grams
of moisture per gram of solid per second, and preferably between
about 0.06 grams of moisture per gram of solid per second and about
0.18 grams of moisture per gram of solid per second.
52. (canceled)
53. The method of claim 46 wherein said explosive dehydration at
step b) comprises a second dehydration rate of between about 0.004
grams of moisture per gram of solid per second and about 0.08 grams
of moisture per gram of solid per second, and preferably between
about 0.01 grams of moisture per gram of solid per second and about
0.06 grams of moisture per gram of solid per second.
54. (canceled)
55. The method of claim 46 wherein said explosive dehydration at
step b) further comprises a third dehydration rate of between about
0.0005 grams of moisture per gram of solid per second and about
0.03 grams of moisture per gram of solid per second, and preferably
between about 0.002 grams of moisture per gram of solid per second
and about 0.02 grams of moisture per gram of solid per second.
56. (canceled)
57. The method of claim 46 wherein oil is added to said slices
prior to step b).
58. The method of claim 57 wherein the oil is conditioned prior to
use as an additive, thereby increasing the fried characteristics
provided by the added oil.
59. (canceled)
60. The method of claim 46 wherein said blanching at step a)
comprises dry blanching, or wet blanching, or oil blanching,
wherein said oil blanching comprises a warm oil dip.
61. The method of claim 60 wherein further the food slices are
subjected to a de-oiling step after the oil blanching of step a)
and before the dehydrating of step b).
62. The method of claim 61 wherein the food slices are subjected to
a pre-drying step after the de-oiling step and prior to the
dehydrating of step b).
63. The method of claim 62 wherein said pre-drying occurs in a
microwave pre-dryer.
64. The method of claim 62 wherein said pre-drying takes from about
5 seconds to about 90 seconds, and preferably from about 10 seconds
to about 20 seconds.
65. (canceled)
66. The method of claim 62 wherein at least one quarter of the
water content of the food product is removed during pre-drying.
67. The method of claim 46 wherein said explosive dehydration at
step b) occurs in a rotary microwave.
68. The method of claim 46 wherein step b) further comprises
dehydrating to a moisture content of between about 3% and about
15%, and preferably between about 6% and about 10%.
69. (canceled)
70. The method of claim 46 wherein step b) occurs under vacuum.
71. The method of claim 46 wherein one or more of said slices in
step a) is a food product consisting primarily of a food material
selected from the group of corn, waxy corn, oats, wheat, sorghum,
rice, waxy rice, kidney beans, pinto beans, lentils, chickpea,
potato, Jerusalem artichoke, yam, tapioca, yucca, tarot, sweet
potato, beet, carrot, arrowroot, cassava, and parsnip.
72. The method of claim 46 further comprising the step of adding a
real food ingredient prior to step b).
73. The method of claim 46 wherein step b) further comprises
dehydrating said slices to a starch melting point range in a
non-oil heating medium in less than about 60 seconds and further
dehydrating said slices in a non-oil medium starch glass transition
range in less than about an additional 50 seconds, and preferably
to a starch melting point range in a non-oil heating medium in less
than about 40 seconds and further dehydrating said slices in a
non-oil medium starch glass transition range in less than about an
additional 30 seconds.
74. (canceled)
75. The method of claim 46 further comprising the step of: c)
further dehydrating said slices in a non-oil medium to a moisture
content of less than about 3%.
76. The method of claim 75 wherein said non-oil medium at step c)
comprises infrared radiation, or microwave radiation, or hot
air.
77. (canceled)
78. (canceled)
79. The method of claim 46 wherein said blanching step a) comprises
a flash fry for about 7 seconds to about 20 seconds in oil having a
temperature of about 120.degree. C. to about 180.degree. C., and
preferably for about 15 seconds to about 20 seconds in oil having a
temperature of about 150.degree. C. to about 160.degree. C.
80. (canceled)
81. (canceled)
82. (canceled)
83. (canceled)
84. The method of claim 60 wherein said warm oil dip is of about 60
to about 120 seconds in duration and wherein said food slice is
brought to a temperature of about 60.degree. C. to about 99.degree.
C. during said blanch.
85. The food slice prepared by the method of claim 46.
86. A method for determining how to reproduce the characteristics
of a desired cooked food product, said method comprising the steps
of: a) determining the moisture level in the desired food product
at a plurality of points in time during the time that the food
product is cooked; and b) using the determined data of step a) to
identify product transition cooking phases during dehydration.
87. The method of claim 86 wherein the identifying of product
transition cooking phases during dehydration of step b) further
comprises identifying a plurality of cooking phases, said cooking
phase consisting of at least a first phase and a second phase, and
wherein further each phase consists of a determined average
dehydration rate and duration.
88. The method of claim 87 further comprising the steps of: c)
determining power inputs required from non-oil cooking to maintain
the determined dehydration rates for at least the first phase and
second phase of step b) for cooking said food product in a non-oil
medium.
89. The method of claim 88 wherein the power inputs of step c)
during the first and second cooking phases comprises microwave
energy.
90. The method of claim 87 wherein the dehydration rate of the
first phase identified in step b) is between about 0.02 grams of
moisture per gram of solid per second and about 0.20 grams of
moisture per gram of solid per second, and preferably between about
0.06 grams of moisture per gram of solid per second and about 0.18
grams of moisture per gram of solid per second.
91. (canceled)
92. The method of claim 87 wherein the dehydration rate of the
second phase identified in step b) is between about 0.0004 grams of
moisture per gram of solid per second and about 0.08 grains of
moisture per gram of solid per second, and preferably between about
0.01 grams of moisture per gram of solid per second and about 0.06
grams of moisture per gram of solid per second.
93. (canceled)
94. The method of claim 87 wherein each phase identified in step b)
is defined at an end point by at least one starch transition
point.
95. The method of claim 86 wherein the food product of step a)
consists of slices of a starting food material selected from the
group consisting of potato, sweet potato, yam, beet, carrot, corn,
parsnip, chickpea, lentils, kidney beans, soy beans, yam, tapioca,
yucca, tarot, arrowroot, cassava, rice, oats, wheat, sorghum, rice,
millet and rye, and/or comprises dough that is fried, wherein said
dough comprises a food material selected from the group consisting
of carrots, parsnip, sweet potato, turnip, squash, courgette,
asparagus, mushroom, broccoli, cauliflower, sweet pepper, chili
pepper, peas, sweetcorn, celeriac, tomato, olives, aubergine,
beetroot, fennel, onions, spinach, chard, cabbage, almonds,
peanuts, walnuts, pecans, brazils,pumpkin, sunflower, sesame,
poppy, squash, peas, chickpeas, lentils, pinto beans, kidney beans,
broad beans, butter beans, soy beans, runner beans, black eye
beans, oats, wheat, sorghum, rice, millet, rye, barley, basil, bay
leaves, coriander, mint, cumin, garlic, lemongrass, oregano,
paprika, turmeric, parsley, pepper, and mixtures thereof.
96. (canceled)
97. (canceled)
98. The method of claim 86 wherein the food is cooked during step
a) using energy transfer to the food product and wherein further
said energy transfer comprises microwave energy.
99. (canceled)
100. The method of claim 88 further comprising the steps of: d)
applying the determined power inputs of step c) to a product in
order to replicate the characteristics of a desired cooked food
product.
101. The method of claim 100 wherein said food product is subjected
to a blanching step prior to step d), wherein said blanching step
comprises a wet blanch, or dry blanch, or oil blanch.
102. (canceled)
103. (canceled)
104. (canceled)
105. (canceled)
106. The method of claim 101 wherein said oil blanching step
comprises a warm oil dip is of about 60 to about 120 seconds in
duration and wherein said food slice is brought to a temperature,
of about 60.degree. C. to about 99.degree. C. during said
blanch.
107. The method of claim 101 wherein oil is added to the food
product prior to step d).
108. The method of claim 107 wherein said oil is conditioned prior
to its addition to the food product.
109. The food product produced by the method of claim 100.
110. The food product of claim 109 wherein said food product
comprises a par-dried half-product, wherein further said
half-product is packaged for later finish drying by a consumer of
said food product.
111. (canceled)
112. A microwave apparatus for continuous deep bed drying of a food
product, said apparatus comprising: an enclosure into which the
food product is continuously introduced and in which microwave
energy is contained, wherein said enclosure comprises a means for
tumbling said food product while said food product is introduced
into said enclosure.
113. The apparatus of claim 112 wherein said means for tumbling
comprises a catenary belt or a rotating drum within the enclosure
and further wherein said enclosure is static.
114. The apparatus of claim 113 wherein said apparatus further
comprises an inlet microwave choke through which the catenary belt
enters the enclosure and an outlet microwave choke through which
the catenary belt exits the cavity.
115. (canceled)
116. (canceled)
117. The apparatus of claim 112 wherein said means for tumbling
comprises a rotating enclosure.
118. The apparatus of claim 117 wherein said apparatus further
comprises at least one microwave choke point exterior to said
rotating enclosure through which the food product traverses.
119. The apparatus of claim 117 wherein said apparatus further
comprises a non-stick metal tumbling surface or a polymer sleeve
insert.
120. (canceled)
121. The apparatus of claim 112 wherein said apparatus further
comprises a plurality of enclosures in series connected to another
by microwave chokes.
122. (canceled)
123. A method for continuous deep bed drying of a food product,
said method comprising the steps of: a) introducing a food product
through a microwave choke and then into an enclosure; b) applying
microwave energy to the food product while said food product is
within said enclosure; and c) tumbling said food product
simultaneously with the application of microwave energy of step b)
and simultaneously with the introduction of food product of step
a).
124. The method of claim 123 wherein step b) comprises applying at
least two different levels of microwave energy to the food product,
depending on the location of the food product within the
enclosure.
125. The method of claim 123 wherein step c) further comprises
tumbling said food product with a modular belt or a rotating drum
within a static microwave enclosure or a rotating microwave
enclosure.
126-151. (canceled)
152. The method of claim 1 further wherein the food product of step
b) comprises a fabricated food slice made from a dough having a
thickness of 1 mm to 4 mm.
153. The method of claim 152 wherein said dough comprises a
moisture content of at least 65% on a wet basis.
154. The method of claim 46 further wherein the food product
comprises a fabricated food slice made from a dough having a
thickness of 1 mm to 4 mm.
155. The method of claim 154 wherein said dough comprises a
moisture content of at least 65% on a wet basis.
Description
[0001] This application is a 371 National Phase filing under
Chapter II of International Application No. PCT/US2007/073820 filed
18 Jul. 2007, which is a continuation-in-part of co-pending U.S.
patent application Ser. No. 11/458,592 filed on Jul. 19, 2006, and
co-pending U.S. patent application Ser. No. 11/686,027 filed on
Mar. 14, 2007.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field
[0003] The present invention relates to an improved method for
producing shelf-stable snack foods and especially low oil snack
foods. More specifically, the present invention relates to a method
whereby a unique combination of unit operations are used to produce
a low-fat potato crisp having organoleptical properties similar to
those of traditional fried potato crisps.
[0004] 2. Description of Related Art
[0005] Conventional potato crisp products are prepared by the basic
steps of slicing peeled, raw potatoes, water washing the slices to
remove surface starch, and frying the potato slices in hot oil
until a moisture content of about 1-2% by weight is achieved. The
fried slices can then be salted or seasoned and packaged.
[0006] Raw potato slices normally have a moisture content from
about 75% to about 85% by weight depending on the type of potato
and the environmental growing conditions. When potato slices are
fried in hot oil, the moisture present boils. This results in burst
cell walls and the formation of holes and voids which allow for oil
absorption into the potato slices yielding oil contents ranging
from about 30% to about 45% by weight.
[0007] The oil content of potato crisps is important for many
reasons. Most important is its contribution to the overall
organoleptic desirability of potato crisps, however, from the
standpoint of good nutrition, it is desirable to maintain a low
level of oil or fat in potato crisps. Many health conscious
consumers desire a low fat alternative to the traditional fried
crisp having minimal taste differences from the fried product.
[0008] Further, a high oil content renders the crisps greasy or
oily and hence less desirable to the consumer. Numerous attempts
have been made in the prior art to reduce the oil content in potato
crisps. Many attempts involve thermally processing the potato
slices in an oven or a microwave to avoid the addition of oil to
the potato crisp.
[0009] For example, U.S. Pat. No. 5,292,540 claims a process for
preparing potato crisps by first pre-baking the potato slices at a
temperature of between about 121.degree. C. to about 260.degree. C.
(250.degree. F. to 500.degree. F.) to remove about 50% to about 80%
of the moisture in the slice prior to microwave heating the potato
slices.
[0010] Similarly, U.S. Pat. Nos. 5,180,601; 5,202,139; and
5,298,707 all relate to a method and apparatus for producing
fat-free snack crisps. For example, U.S. Pat. No. 5,298,707
discloses a first intensive microwave pre-baking step that reduces
the moisture content in the potato to about 25% to about 30% by
weight. The '707 Patent employs a special intermittent microwave
field provided by a meandering wave guide and a special conveyor
belt to reduce the problems of hard surface and texture. However,
according to U.S. Pat. No. 5,676,989, the approach disclosed in
U.S. Pat. No. 5,298,707, still produces an undesirable, relatively
dense, hard crisp. Similarly, nearly all of the prior art processes
result in a low fat snack food having organoleptical properties far
less desirable than the fried potato crisp counterpart. Thus, none
of the prior art solutions have succeeded in mimicking the taste
and texture of fried potato crisps.
[0011] Consequently, a need exists to provide an economical method
for making reduced oil potato crisps having desirable
organoleptical properties similar to traditional potato crisps.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The novel features believed characteristic of the invention
are set forth in the appended claims. The invention itself,
however, as well as a preferred mode of use, further objectives and
advantages thereof, will be best understood by reference to the
following detailed description of the illustrative embodiments when
read in conjunction with the accompanying drawings wherein:
[0013] FIG. 1 is a flow chart representation depicting numerous
embodiments of the present invention;
[0014] FIG. 2 is a graphical representation of the dehydration and
temperature profile of a plurality of potato slices undergoing an
explosive dehydration step in accordance with one embodiment of the
present invention;
[0015] FIG. 3 is an alternative graphical representation of the
dehydration profile depicted in FIG. 2;
[0016] FIG. 4 is a graphical representation of the dehydration
profile of a plurality of potato slices in accordance with one
embodiment of the present invention;
[0017] FIG. 5 is an approximate comparative graphical
representation of the data depicted in FIG. 3 and FIG. 4;
[0018] FIG. 6 depicts a prior art dehydration profiles of
continuously fried potato slices and batch kettle fried potato
slices; and
[0019] FIG. 7 is a schematic perspective representation of one
embodiment of the catenary belt microwave described herein with a
cutaway showing the interior of the microwave cavity;
[0020] FIG. 8 is a schematic cross-section representation of an
alternative embodiment of the catenary belt microwave described
herein; and
[0021] FIG. 9 is a schematic perspective representation of the
rotating cavity microwave oven described herein.
DETAILED DESCRIPTION
[0022] FIG. 1 is a flow chart representation depicting the
preparation steps of raw food-based slices in accordance with
numerous embodiments of the present invention. The preferred
sources of food substrates or slices are cereal grains (e.g., corn,
waxy corn, oats, wheat, sorghum, rice, oats, millet, rye, barley,
and waxy rice), pulses (e.g. kidney beans, pinto beans, lentils,
chickpea), tubers (i.e., potato, Jerusalem artichoke, yam), fruit,
vegetables, and roots (i.e., tapioca, yucca, tarot, sweet potato,
beet, carrot, arrowroot, cassava, parsnip). In one embodiment of
the present invention, potatoes of the chipping variety can be
used. Potatoes of the chipping variety that can be used include,
but are not limited to Saturna, Lady Rosetta, Lady Clair, Hermes,
Maris Piper, Erntestolz, Agria, Atlantic, Monona, Norchip, Snowden,
Kennebec, Oneida, and Tobique. Non-chipping potato varieties can
also be used including, but not limited to Marfona, King Edward,
Yukon Gold, Desiree, Karlena and Estima. Similarly, French fry
varieties such as Russet Burbank, and Bintje can be used. It should
be noted that while chipping potatoes typically used for making
potato crisps have relatively low levels of reducing sugars, and
are not typically used to make French fries or baked potatoes, any
potato can be used in accordance with the present invention and the
present invention is not limited by physiological or biological
make up of the potato.
[0023] Although potato slices are used to illustrate this
invention, one skilled in the art armed with the knowledge of this
disclosure will recognize that the resultant processing times and
temperatures disclosed below may need to be adjusted to compensate
for the use of a different starting material. For example, while
the present invention is suitable for the preparation of low-fat
potato crisps made from potatoes, the present invention is also
applicable to a wide variety of food substrates which can be cut or
otherwise formed into flat, generally thin slice-shaped portions.
The present invention can be used to prepare crisps from raw
vegetables, such as potatoes, and the like that have been cut into
slices or, alternatively, doughs comprising masa, other raw
materials reduced to a formable state, re-hydrated dry ingredients
including potato flakes, or other food substrates may be ground
into a dough or paste, mixed with other ingredients and additives
and then shaped into configurations such as flat slice or cracker
shapes for preparation into a snack. Consequently, as used herein,
the term "food slice" encompasses pre-forms made from a dough.
[0024] Similarly, while the present invention is suitable for the
preparation of low-fat potato crisps made from sliced potatoes, the
resultant processing times and temperatures disclosed below may
need to be adjusted to compensate for the use of a different
starting material and shape. For example, potatoes can be cut into
slices having one or more flat sides or the potatoes can be sliced
with one or both ridged sides. One advantage of ridged sliced
potatoes is that the slices are less likely to stick together
because of the reduced surface tension, which results from a
reduced surface area available for contact between the slices.
Consequently, less intensive surface drying may be required with a
ridged slice. In addition, when a continuously agitated drying
system such as a rotating drum is used, the profile of a ridged
slice can impart greater resistance to mechanical folding or
clumping actions thus producing a higher proportion of singulated
whole slices and a lower proportion of excessively folded
slices.
[0025] In one embodiment, the potatoes can be cut into wedges or
French fry-like sticks of suitable size. In one embodiment,
French-fry like sticks have cross-sectional widths of about 5 to
about 6 millimeters. In another embodiment, potatoes are cut into
slabs of, for example, about 1 to about 3 mm depth, about 50 to
about 100 mm length and about 20 to about 50 mm width or other
suitable size known in the art. Because the French-fry like sticks,
wedges, and slabs have different geometries, surface area to volume
ratios, etc. than slices, the processing times and energies
disclosed in each unit operation below may require adjustments.
Similarly, if the starting material is further reduced in size (for
example by comminution through grating, shredding, ricing, milling
or grinding) and then reformed to a dough, pellet, cluster,
laminated snack or snack cake comprising the original material and,
optionally, a medley of additional ingredients, the resulting food
slice can be processed to a desirable snack product under
appropriate conditions using the knowledge of this disclosure.
Methods for preparing various pre-forms are known in the prior art
as exemplified by U.S. Patent Application Publication No. US
2005/0202142, which discloses a method for making a clustered snack
product or U.S. Patent Application Publication No. 2002/0142085,
which discloses a method for making a potato mash that is suitable
for the production of food products, including potato snacks.
[0026] In one embodiment, saturna or other suitable potatoes are
washed and peeled prior to the slicing step. Although peeling is
optional, the peel can contribute to a dominant earthy flavor when
the finished food product has low oil content. In one embodiment,
the potatoes are sliced to a thickness of between about 1.0
millimeters to about 2.5 millimeters (0.040 inches and about 0.1
inches) in a slicer to provide a plurality of potato slices. Other
suitable slice thicknesses may be selected. The potatoes can be dry
sliced, sliced in the presence of water, sliced in oil which may
provide a desired oil addition to the slice and/or accomplish an
oil blanching step. In one embodiment, potato slices are washed in
a flume and dewatering belt to remove surface starch, scraps and
excess oil, if applied, from the potato slices.
[0027] The potato slices are then blanched. If a dough is used, the
blanching step may have already occurred at a prior processing
stage and additional blanching may not be necessary. If the
blanching occurred in a prior processing stage, then the blanching
step should be construed to have occurred within the meaning of
claimed limitations of the present invention. Further, in a
dough-based embodiment, any blanching step is optional. Blanching
is only a requirement where the product can benefit from
pre-cooking the native starch or de-activating enzymes. Blanching
is not necessary for leaching sugars or where native starch is
already hydrated or when enzymes have been deactivated in a prior
processing step. For example, in one embodiment, steam cooked
vegetables such as carrots can be used as the food slice and no
further blanching step is necessary. The purpose of the blanching
step is to deactivate enzymes such as peroxidase, polyphenol
oxidase, and lipoxygenase that can cause undesirable "earthy green"
flavors. In one embodiment, blanching can also be used to hydrate
the native starch of the food slice. Blanching can be accomplished
in a number of ways, including a wet blanch 110, a dry blanch 112
or an oil blanch 114. The blanching medium temperature and dwell
time can vary based upon the shape and cross section of the food
slice and are preferably such that the potato slices are
sufficiently cooked to deliver a clean base flavor, absent of any
raw, green taste.
[0028] In one embodiment, the slices are dry blanched 112 at a
slice temperature of about 90.degree. C. to about 95.degree. C. for
about 10 to about 120 seconds and more preferably for about 90 to
about 100 seconds by a rotary or conveyor infrared dryer or other
suitable heating medium. Dry blanching is advantaged for starchy
food slices since it avoids the introduction of moisture that may
gelatinize starch and create difficulty due to adhesion of the food
slice to other slices or surfaces during processing. In one
embodiment, dry blanching 112 is performed through conduction, for
example using heated conductive rollers or a heated flat ceramic or
metal pan that may contact both sides of the slice simultaneously
for 10 seconds to 90 seconds depending on the processing
temperature in use, which will typically be about 60.degree. C. to
160.degree. C. For thin food slices temperatures of 90.degree. C.
to 120.degree. C. are preferred for 30 to 90 seconds. Contacting
both sides of the slice simultaneously ensures there is no lift or
curl of the food slice away from the conductive surface, which can
reduce the effectiveness of blanching. Optionally, the plate may
comprise a textured metal surface, for example as supplied by
RIMEX, or a non stick coating to improve slice handling. At higher
temperatures surfaces may be perforated to ease escape of steam. In
an alternative embodiment dry blanching is achieved with microwaves
or comprises irradiation. Dry blanching 112 of other shapes such as
French fry like sticks can require blanching of two to four minutes
and selection of appropriate infra-red wavelength for adequate
penetration of the food slice. After dry blanching 112, the food
slices can optionally be pre-dried 152 in a forced air oven to
remove some initial water to improve overall process efficiency.
The dry blanched 112 slices can then be routed to the oiling step
160, discussed below.
[0029] In one embodiment, the food slices are oil blanched 114 by
placing the slices into a warm oil flume, a batch kettle or a
continuous oil dip. ABCO, LYCO, PPM and Heat and Control are
examples of manufacturers of commercial blanching equipment, which
is commonly used in the food industry that can be adapted in either
rotary or linear form to oil blanching described here. A linear
water blancher available from Heat and Control that uses a
caterpillar conveyor with vanes to move slices through the bath in
compartments can be adapted to a suitable oil bath and will
preferably use mild agitation only. A HEATWAVE frying system
available from Heat and Control of Hayward, Calif. USA can also be
used. In one embodiment, slices are spread evenly distributed
across the exit conveyor of the oil blancher for presentation to
the next unit operation.
[0030] In the prior art, oil blanching is typically done at
relative high temperatures, such as 150.degree. C. and above. For
example, U.S. Pat. No. 5,204,133 titled "Process for Preparing
Sliced Potato Products" and issued on Apr. 20, 1993, discloses an
oil blanching temperature of about 360.degree. F., or 182.degree.
C., at Column 4, Line 55. Likewise, U.S. Pat. No. 4,608,262 titled
"Method of Making Frozen Potato Patties and the Products Formed
Thereby" and issued on Aug. 26, 1986, discloses oil blanching
temperatures ranging from about 325.degree. F. to about 380.degree.
F., and preferably about 350.degree. F. to 370.degree. F., at
Column 3, Lines 7-8. What Applicants refer to generally herein as
an "oil blanch" is more specifically to Applicants` invention a
"warm oil dip." Such warm oil dip is considered to be a time based
heat treatment where the heat and time combination is sufficient to
inactivate enzymes and to hydrate (`cook`) native starch but is
below the evaporation temperature of water in the blanching vessel.
Therefore, at sea level, standard atmospheric pressure the maximum
oil temperature used for Applicants' warm oil dip is about
99.9.degree. C. In one embodiment, the food slices are blanched at
a temperature that enables the native starch to be hydrated (fully
or partially gelatinized) by the inherent moisture of the potato
slice. A final slice temperature of about 70.degree. C. to about
99.degree. C. during a warm of dip of about 60 to about 120 seconds
in duration, or more preferably, for a thin food slice, a final
slice temperature of about 90.degree. C. to about 95.degree. C. for
90 second dip is sufficient for optimal flavor benefit, slice
rigidity and subsequent handling. A warm oil dip oil temperature
ranging from about 60.degree. C. to about 99.degree. C. with a warm
oil dip duration of between about 30 seconds to about 300 seconds
is preferred by Applicants for the processes described herein. More
preferable is a warm oil dip oil temperature of about 75.degree. C.
to about 99.degree. C. with a duration of about 50 seconds to about
150 seconds. The most preferred ranges for Applicants' warm oil dip
are an oil temperature of about 85.degree. C. to about 95.degree.
C. for a duration of about 60 seconds to about 100 seconds.
[0031] An advantage of oil blanching with a warm oil dip is to
preserve minor constituents of the food slice that make important
contributions to flavor and color that may be solubilised or
otherwise impaired if using conventional water or steam blanching.
Although no frying is involved, the technique of oil blanching as
disclosed here brings the flavor of the finished chip much closer
to its fried counterpart when compared to other blanching methods
that may be used to produce products with similar oil contents. In
this way, the oil blanching 114 method using the unique warm oil
dip time and temperature disclosed here overcomes a significant
hurdle to the taste acceptability of reduced oil, non-fried food
slices disclosed in the prior art, which either suffer from raw and
green notes due to the absence of any blanching method or suffer a
foreshortened shelf life due to the degradation of flavor caused by
conventional blanching methods or oxidation after processing.
[0032] Applicants' warm oil dip has been shown to protect the
sensitive, polyunsaturated lipids that are naturally present in the
substrate materials of the food slice from degradation. Degradation
results in undesirable flavors, particularly those derived through
oxidation pathways, in the finished chip and can arise from
oxidative or hydrolytic stress caused by the processing conditions
or arise in the finished, reduced oil food slice during storage in
a pack due to oxidation of, for example, potato lipids, rice lipids
or soy lipids. Therefore, an advantage of the warm oil dip is to
extend the shelf life of packaged potato chips, from as little as
two to four weeks when using conventional blanching methods for
example water or steam, to the norms associated with the packaged
snacks category in FMCG markets.
[0033] Without being bound by theory, the inventors believe the oil
dip is a low stress processing method that minimizes exposure to
enzymatic, hydrolytic or oxidative reactions of lipids in the food
slice and subsequently provides a protective coating at the
cellular level of the food slice once in its finished chip form.
Therefore, an advantage of the warm oil dip is to control the
contribution of flavors derived from the food slice substrate and
the food slice oil to the final chip so that each component
contributes an optimum balance of flavors to the final chip. When
the food slice substrate is potato, the warm oil dip suppresses
undesirable flavor reactions, in particular potato lipid oxidation,
and promotes desirable flavor reactions. The relative contribution
of flavor compound classes comprising, but not limited to,
aldehydes, strecker aldehydes, ketones, alcohols, alkyfuran or
pyrazines can be positively influenced with the processing method
disclosed.
[0034] Those skilled in the art will understand that the use of a
warm oil dip to influence pyrazines can also be applied to
influence and minimize similar chemical reaction pathways, for
example acrylamide formation, for which pyrazine is sometimes used
as a chemical marker. Without being limited by theory, the
Applicants believe that the warm oil dip method influences the
availability of reactants in the food slice base to participate in
reactions commonly associated with food cooking and drying and in
particular potato food chemistry. For example, swelling of the
potato starch may cause immobilization or partial immobilization of
the cell wall constituents in a potato slice. When potato slices
are treated by the oil dip the loss of water-soluble constituents
such as sugars, which are essential to the desirable final color
and flavor of the potato chip, are avoided. Equally, the loss of
crispness in texture that is typically associated with potato chips
that have been blanched with hot water is avoided. Therefore, the
potato slices are still suitable for drying in a conventional
continuous or batch fryer to make a potato chip to the standard
expected by consumers of high quality brands such as Lays potato
chips today.
[0035] The flavor benefit is clearly noticeable to consumers of
potato chips when steam, the best blanching method known in the art
for manufacturing low oil potato chips, is compared to the warm oil
dip. In multiple tests, consumers who ate salted potato chips
treated with steam prior to explosive drying scored the product 6.1
to 6.4 for overall liking on a 9 point scale, whereas, salted
potato chips prepared by treatment with a warm oil dip scored
6.8-6.9. When consumers compared potato chips made by these two
methods, 66% preferred the chips made from the warm oil dip. This
statistically significant preference is attributable to the flavor
difference between the products evidenced by the significantly
different liking scores found in favor of chips made using a warm
oil dip versus a steam blanch for overall flavor (7.1:6.3) and
aftertaste (6.4:5.9) using the 9 point scale. Therefore, an
important benefit of the warm oil dip is to enable a non-fried
potato chip with an oil content less than 15% to be optimized for
consumer appeal. A potato chip made with half the fat of regular
potato chips using the Applicants' disclosure will be perceived by
consumers to have an overall acceptability that is not
significantly different to Lays, the best selling potato chip brand
worldwide.
[0036] The warm oil dip is suitable as a pre-treatment step to
non-fried and fried snack food production. The warm oil dip can be
used as the blanching step to process whole, cubed or other diced
forms of vegetable or potato to make a pre-form dough for this
invention. The dough can then be formed and explosively dried in a
microwave oven as disclosed in this invention. Further, the warm
oil dip can replace conventional blanching methods in the
production of frozen potato products or potato flakes and granules
and other potato products that are subject to lipid oxidation. The
warm oil dip could substitute both or either of the pre-cooking
(typically around 70 to 75 Celsius) and cooking (typically at or
approaching 100 Celsius) steps commonly performed using steam in
flakes, granules, french fries and croquettes production today.
[0037] Applicants' warm oil dip also acts as an oil addition step
to the raw slice. Using one of the subsequent de-oiling methods
disclosed in this invention the ingress of oil into the food slice
during dehydration can be controlled to a specified level. A
further advantage of oil blanching with a warm oil dip is to avoid
presenting excess water to the starch in the food slice and
therefore to minimize gelatinization of surface starch, which can
assist with subsequent handling. Even though temperatures are
maintained below water evaporation temperatures, oil blanching with
a warm oil dip can result in some moisture loss from the food
slices. This is thought to be due to free water in or on the food
slice being displaced into the oil. The amount of water displaced
will in part be dependant on the amount of free water on the food
slice before oil blanching. Therefore, it is preferable to remove
as much free water as possible before a food slice enters the oil
blanching step 114.
[0038] To achieve this, surface drying techniques disclosed later
in this invention can be applied before oil blanching. Since the
blanching temperature is lower than the boiling point of water,
water may become suspended or emulsified in the oil. In this
situation the processor may elect to use a settling sump or similar
device in order to drain the water or divide oil which is
circulating so that a portion is routed through an evaporation
chamber heated at >100.degree. C.
[0039] In one embodiment, the slices are treated by flash frying
for a suitable time and temperature to deactivate enzymes in place
of oil blanching. Flash frying is considered to be a time based
heat treatment where the heat and time combination is sufficient to
inactivate enzymes and evaporate a portion of water in the flash
frying vessel. Therefore the minimum flash frying temperature is
that at which the water inside the potato cell matrix boils,
commonly observed to be 100.degree. C. at standard atmospheric
pressure. Similar equipment to that used for oil blanching can be
used for flash frying. For example, in one embodiment, potato
slices are flashed fried for about 7 seconds to about 10 seconds in
oil at about 180.degree. C. Alternatively, the potato slices can be
flashed fried for about 15 to about 20 seconds in oil having a
temperature of about 150.degree. C. to about 160.degree. C. These
conditions may be preferred for thicker food slices to ensure
adequate heat transfer and slice rigidity for subsequent
handling.
[0040] More moisture is lost if the oil blanching step 114 is
replaced by flash frying. For example, in one embodiment, flash
fried slices comprise a moisture content of about 50% to about 55%
by weight. Consequently, in one embodiment, about 30% to about 40%
of the starting weight of moisture in a potato can be lost when the
oil blanching step 114 is replaced by flash frying, which can
improve overall process efficiencies. One benefit of flash frying
is to simultaneously deactivate enzymes, add a limited amount of
oil to the food slice and pre-dry the substrate in one step.
Finished chip oil content can be controlled using one of the
subsequent deoiling methods disclosed in this invention.
[0041] Any oil or fat is suitable for the process disclosed
including vegetable oil, animal fats or synthetic oils, for example
coconut oil, corn oil, cottonseed oil, palm oil, palm olein,
safflower oil, high oleic safflower oil, palm stearin, soybean oil,
olive oil, rice bran oil, sunflower oil, mid or high oleic
sunflower oil, rape seed oil, lard, tallow, Olestra.TM., sucrose
polyesters, medium chain fatty acids or a blend of different oils.
The choice of oil can be used to influence the final flavor and
mouth feel of the finished crisp as well as the nutrition profile.
Selecting an indigestible oil (e.g. Olestra.TM.) enables the
manufacture of snacks with a lower calorific density than
conventional snack foods, if combined with a food slice of suitable
composition.
[0042] The slice can then be de-oiled 142 to the desired level. Oil
removal is assisted by the wet and raw to partially cooked nature
of the food slice because the oil is principally on the slice
surface and has not been substantially absorbed into the slice
interior. The slice is preferably de-oiled directly from the warm
oil dip while hot but can be cooled to a temperature at or below
ambient before de-oiling.
[0043] De-oiling can be performed using wet methods. In one
embodiment the de-oiling step 142 can occur in a linear steam
blancher commercially available from ABCO, where the food slices
are transported through a chamber filled with atmospheric pressure
steam by a series of steam manifolds above and below the belt. A 20
to 60 second exposure time using this method is sufficient to
de-oil a thin food slice to less than 18% oil, less than half the
fried counterpart, and typically to around 12% oil in the final
chip. Alternatively, the slices can be transported through a
perforated rotating drum made from metal or a suitable heat
resistant polymer (e.g. polypropylene or PTFE). Steam can be
introduced via a manifold inserted along the center of the rotating
drum, alternatively the drum can be mounted inside a chamber with
circulating steam. Sparging the tumbling slices with steam at 0.7
bar for 20 seconds is sufficient to fully de-oil to 3% or less in
the final chip. Mounting an external steam or air knife angled
toward the outer circumference of the drum will assist this process
step by dislodging any slices that stick to the internal
circumference of the drum.
[0044] In one embodiment, the de-oiling step 142 can occur by
washing in a hot water bath (typically about 50.degree. C. to about
65.degree. C.) or ambient cold water bath (typically about
15.degree. C. to about 25.degree. C.) either of which optionally
may contain marinade ingredients. This de-oiling method removes all
available surface oil to so that a thin potato slice, which is
subsequently dried, will typically contain less than or equal to 3%
oil. A model No. PSSW-MCB speed washer available from Heat and
Control is one example of a suitable water bath. Similar results
are achieved if the water bath is combined with or replaced by a
series of pressurized water jets or knives mounted above and below
the slices, which are transported on an open weave conveyor that
may optionally use an upper hold down conveyor. The advantage of
water jets is to provide more control over de-oiling through
variables such as water flow rate, water pressure, angle of water
knife and exposure time.
[0045] Water jets are an efficient method of de-oiling to low oil
contents. Levels less than 3% oil are feasible and a range of 5% to
10% can be achieved in the finished chip with acceptable process
control. In one preferred embodiment, a water knife positioned
transversely above and below the food slice product transport belt
can be used to wash oil from the surfaces of the slices. After the
water knife, a high velocity air knife system, for example the Heat
and Control Air Sweep commonly used for de-watering during potato
chip processing, is preferably used to remove any excess water or
oil mix on the slice. A water flow rate of less than 0.25 liters to
3 liters of water per minute per nozzle or preferably 0.5 to I
liters per minute per nozzle is typically sufficient for controlled
oil removal to 5% to 10% oil content in the finished chip.
Effective de-oiling can be achieved with contact times between the
food slice and water knife of around 0.25 seconds to 1 second,
which is approximately 2 to 4 meters per minute on a belt conveyor.
Longer exposure times, for example 5 seconds, or higher water flow
rates, for example 6 liters per minute, are feasible but only
necessary when very low oil levels, for example less than 3%, are
required.
[0046] To reduce the amount of water used or to avoid removing too
much oil, a water spray comprising a mist of fine droplets of water
can be applied to the food slice to act as a gentler de-oiling
media. This effect can be demonstrated with a handheld garden spray
or by adding compressed air to the water spray nozzle. Water
temperature can be varied to suit the food slice being processed
however ambient to cool water is preferred for starchy food slices
like potato that are susceptible to gelatinization in contact with
excess warm or hot water. Water and oil pooled on top of the slices
after passing through the water knife or water spray is very mobile
and can either be drained or very easily blown or sucked off the
food slice surfaces with air knives and or vacuum suction above or
below the food slices. Controlled exposure to water in this way
does not require a monolayer presentation of food slices to
successfully de-oil and the use of air knives is sufficient to
separate the slices to remove remaining water/oil mix for further
processing. As with other de-oiling methods, a displaced water/oil
mix can be separated in a settling tank or via centrifuge in order
to quickly reclaim the oil which can then be reused in the oil
blanching step to minimize unnecessary wastage.
[0047] Slices from de-oiling involving wet media can be further
processed using the surface drying and pre-drying methods disclosed
later in this invention. However, for some food slices the
processor may find it preferable to use a de-oiling method that
minimizes or fully eliminates the exposure of the food slice to wet
steam or water. De-oiling in this way can avoid product handling
issues that occur when starch on the surface of a food slice
becomes sticky due to gelatinization in the presence of heat and
water or condensate. In one embodiment an oil knife is used in a
similar way to a water knife in order to dislodge the bulk oil from
the surface of the food slice and replace the surface oil of the
potato slice with a very thin coating of oil. One advantage of the
oil knife method is to avoid the introduction of water, steam or
air that may damage the quality of the oil as it is removed,
gelatinize starch or expose the slice substrate to reactions that
may degrade its flavor.
[0048] De-oiling 142 can be achieved on a linear drain belt which
may optionally be assisted by warm environmental temperatures, for
example 90 C similar to the oil blanch, so that the oil maintains a
low viscosity in order to improve its mobility. Oil mobility on the
slices can be further encouraged by gravity through an incline or
vibration during conveying. This straightforward drainage method
can produce high quality chips with reduced oil contents,
especially when used prior to a pre-dry microwave 154 or explosive
microwave drying step 200 where the internal steam pressure forces
a further proportion of the oil to the surface of the slice from
where it is drained by escaping steam or removed through the
mechanical action of tumbling.
[0049] Blowing cool, ambient, warm or hot air onto the food slice
surfaces can further assist with a simple de-oiling step. This
method can be demonstrated by the use of a hot air paint stripping
gun available at most hardware stores. Air temperatures above 120 C
are most efficient at removing oil with typical airflow rates of
4.5 to 5.5 m/s. High temperatures (e.g. 180 C to 200 C) can cause
surface damage or excessive drying to the food slice and should
therefore be avoided. Air temperature, air velocity at the slice
surface, exposure time and angle of impingement can all be used as
variables to control the amount of oil removed. An exposure time of
5 to 90 seconds or preferably 10 to 20 seconds and an impingement
angle close to 90 degrees is preferred for effectiveness of oil
removal and ease of product handling. Humidification of the air may
further assist the de-oiling process. The de-oiling method may also
be carried out by using a series of pressurized air manifolds or
air knives mounted above and/or below an open mesh transport belt.
Oil contents around half that of fried counterparts can be
achieved. For example a thin potato slice may have finished oil
content after drying of 15% to 18% compared to a fried counterpart
of around 36%.
[0050] To further improve the amount of oil removed when de-oiling,
the manifolds can be fitted with nozzles selected to increase the
degree of impingement of the de-oiling fluid on the food slice
surface. For example, a manifold fitted with slotted nozzles SL31
supplied by Delevan Spray Technologies or VEEJET H1/4USS from
Spraying systems company and mounted almost perpendicular to a
linear transport belt at a distance of 10 mm to 50 mm but
preferably 10 mm to 25 mm above and below the food slice surface
create a physical curtain or knife of gaseous fluid through which
the food slice is transported while the surface oil is held back or
blown back. By adjusting the gaseous fluid pressure, nozzle height,
nozzle impingement angle or exposure time the oil content in the
final chip can be controlled. A manifold pressure of 1.0 to 7.0 bar
but preferably 1.5 to 3.0 bar is sufficient to de-oil a food slice
approximately 15% in 5 seconds contact time for the orientation
described.
[0051] Steam is a more effective method of removing oil than air
and achieves the same oil content more quickly Food slices can be
fully de-oiled with steam in a single pass to less than 3% oil in
the finished chip provided the dc-oiling equipment is maintained
substantially free of excess oil. The exact process conditions must
be optimized for the food slice being treated with longer exposure
times and higher pressures or fluid velocities favoring greater oil
removal. However, a reducing exponential return can be expected
between energy expended and amount of oil removed so the exact
process conditions also depend on the level of oil the food slice
is to be reduced to.
[0052] In a preferred embodiment a steam knife or manifold fitted
with fan shape nozzles, for example SL31 supplied by Delevan Spray
Technologies or VEEJET H1/4USS from Spraying systems company, is
mounted at 20 mm to 30 mm above and below food slices exiting the
warm oil dip. In one embodiment, saturated steam is delivered
through the manifold at 0.5 to 3.0 bar steam pressure to reduce the
oil content to between 14% to 7% by weight of dried food slice.
Food slices may be presented to the single pass steam de-oil
curtain on a belt conveyor traveling at 2 to 4 meters per minute to
give an approximate contact time between slice area and steam of
0.25 seconds to 1 second. Higher steam pressures result in lower
oil contents but obey a power law of diminishing returns whereby
the benefit of further marginal oil reductions for steam pressures
above 3 bar for the manifold height disclosed must be evaluated
versus other effects that may be induced, for example slice
displacement on the conveyor. Longer contact times, or higher water
phase content of the steam can also be used to reduce the oil
content further.
[0053] The de-oiling chamber will benefit from a top and bottom
belt to control food slice transport and maintain good presentation
of the food slice to the de-oiling curtain by minimizing slice
agitation. Continuous belt cleaning and vapor extraction to remove
excess oil will assist with maintaining a clean local environment
in the de-oiler unit, which will benefit the ability of the
processor to control the food slices to the target oil level.
Extraction can be achieved with suction plenums mounted above and
optionally below the transport conveyor. The de-oiling
effectiveness and evenness may also benefit from briefly fluidizing
the slices to aid distribution and separation, for example by
utilizing several manifolds or knives expelling air or another
gaseous fluid before the de-oiling media is encountered. In one
embodiment steam as the de-oiling media is used to fluidize the
slices. The top and bottom belts should be constructed with a large
open mesh area and one or both may optionally have resistant but
compressible properties, provided for example by thin gauge metal
wire or rubber polymer constructs, that assist the distribution of
slices exposed to turbulent conditions caused by air or other
gaseous fluid flows. While pressurized air, superheated steam or
other dry gases are suitable stripping media, steam is preferred as
the most effective gaseous oil-stripping medium.
[0054] Alternative de-oiling media include, but are not limited, to
superheated steam (dry steam) or nitrogen. Superheated steam may be
used at high temperatures, for example 160 C, however marginally
superheated temperatures of, for example, 105 C simplify the
processing requirements. These media offer an advantage over air
since they exclude oxygen from contact with the oil or food slice
surface, which avoids oxidation and preserves quality. Similarly
nitrogen or super heated steam offer an advantage over wet steam
since they exclude water from contact with the oil or food slice
surface, which avoids hydrolysis of oil and preserves food slice
quality. Dry media and wet media may be used on their own or in any
combination with each other for example, and illustration only,
steam stripping followed by nitrogen stripping. The processor may
select the most suitable method taking into account the properties
of the food slice being de-oiled and the oil reduction desired
[0055] In one embodiment steam is reclaimed from the primary
explosive drying step and compressed for use at the de-oiling
step.
[0056] In one embodiment, de-oiling is performed in a rotary
de-oiler to achieve a fat content of less than half the fried
counterpart. The de-oiler may be based on a rotary dryer with a hot
air manifold mounted internally or can be a perforated rotating
drum, that is optionally mounted inside a hot air circulating oven,
and has a directional hot air manifold mounted along its center. As
described above, other media for example nitrogen, steam or
superheated steam may be used as an alternative to hot air.
[0057] In one embodiment, centrifugal de-oiling can be used to
lower the oil content in the de-oiling step 142 to the desired
level. In a further embodiment, de-oiling is achieved through
contact with surfaces that absorb the oil or mechanical skimming of
the slice surface by the use of belts, brushes, rollers or
presses.
[0058] Some food slices, for example starchy potato slices, that
have been de-oiled with hot media will benefit from cooling to
improve subsequent handling in the non-oil drying process.
Therefore, the surface properties of the slice may be modified to
reduce stickiness by cooling and removing condensate from the
slice. Slices may be carried on an open conveyor or passed through
a cooling tunnel. More rapid cooling can be achieved with
pressurized air knives or a series of manifolds operating with
compressed air and optionally equipped with selected nozzles to
increase impingement on the slice surface. A dry medium is
preferred for cooling but can be selected from air, nitrogen, a
combination or other means. Cooling is not a necessary step if food
slices do not exhibit sticky surface properties, for example as a
result of lower starch availability. In this case it is preferable
for energy efficiency to hot transfer the food slices at around 70
C to 90 C into the next processing stage.
[0059] The de-oiling step 142 can be used to dial in and control
the desired oil content to a very narrow range. In One embodiment,
the food slices are de-oiled such that the finished, dried food
product comprises an oil content of less than 3% by weight.
However, less intense de-oiling can deliver higher oil levels in a
controlled manner and in one embodiment, the food slices are
de-oiled to an oil content of less than 10% and preferably between
5% and 8% or to an oil content of less than 15% and preferably
between 11-13% by weight of finished chip. Alternatively, minimal
de-oiling is applied to deliver a slice having about 17% to about
25% oil by weight of the finished chip or a simple drain belt with
no active de-oiling is used to deliver a slice having 25% to 35%
oil by weight of finished chip. Consequently, one advantage of the
oil blanching step 114 using a warm oil dip is the ability to
control the oil levels in a food slice through a combination of the
oil blanching and the de-oiling conditions applied before
drying.
[0060] Food slices prepared using either oil blanching or flash
frying followed by de-oiling and cooling or optionally dc-oiling,
pre-drying and cooling may go on to be fully dried or,
alternatively, may be packed as a half product suitable for
finishing by heating at home or at a secondary location, for
example a vending or catering outlet. Food slices intended for this
application are preferably de-oiled to less than 15% fat and more
preferably to less than 10% fat equivalent of a dried chip. The
advantage of this preparation method is to deliver food slices that
retain a structural oil content that benefits final chip flavor yet
are substantially non-oily and non-adhering on their surface and
therefore are suitable for packaging into known formats that may
optionally use preservative technologies, for example inert gas
flushing, vacuum packing, retort, scavenging or aseptic packing.
Those skilled in the art may recognize that pasteurization or
sterilization of the half-product may be achieved prior to packing
by selection of appropriate time-temperature combinations during
the de-oiling step. The de-oiling step ensures the half-product
retains some oil for flavor but is not significantly oily on the
surface. The half-product cleanly releases from flexible or
semi-flexible packaging structures to individual slices for
convenient finish cooking via the preferred method (for example pan
frying with or without oil, hot air oven, infra-red toasting oven,
steam oven or microwave) at the preferred location (for example at
home or at a vending, catering or snacks manufacturing site). Thus,
one advantage of this preparation method is to enable the end user
to experience a low oil, healthy and convenient hot snack
product.
[0061] Those skilled in the art will recognize that partial drying
of the half-product prepared with this method can further improve
its suitability for packaging and further increase convenience for
the end user. Non-oil par-drying methods, for example baking in a
microwave oven, impingement oven or conventional hot air oven are
preferred and, using the methods described later in this disclosure
the moisture content will preferably be reduced below the starch
melting point, typically less than 1 gram of moisture per gram of
solids in potato based foods, or more preferably below the starch
glass transition point, typically less than 0.25 grams of moisture
per gram of solids in potato based food substrates. One advantage
over heating a half-product compared to a regular dried snack is
that the higher moisture content ensures a more consistent and
pleasant finished snack.
[0062] In an alternative embodiment to dry or oil based blanching,
the potato slices can be wet blanched 110 in water or steam at
about 60.degree. C. to about 100.degree. C. for between about 50
seconds and about 3 minutes depending on the heat transfer required
by the food slice dimensions. For example, a potato stick (French
fry shape) food slice typically requires 3 minutes at about
80.degree. C. to about 90.degree. C. whereas a thin potato slice or
slab typically requires about 90 seconds at about 80.degree. C. to
about 90.degree. C.
[0063] Optionally, after wet blanching 110, the potato slices are
then washed 120 in a water wash to further reduce gelatinized
surface starch. The washing step may use hot water (typically about
50.degree. C. to about 65.degree. C.) to improve starch
solubilisation. In one embodiment, the washing step 120
continuously uses cold water (typically about 15.degree. C. to
about 25.degree. C.) that quenches the blanching process and
improves the crispness of the final product texture, which is
thought to be due to retrogradation of starch components. Either
wash may optionally contain marinade ingredients. Removal of excess
gelatinized surface starch will lessen the tendency of the potato
slices to stick or clump together in later drying steps. A model
No. PSSW-MCB speed washer available from Heat and Control, Inc., of
Hayward, Calif. USA can be used to remove the surface starch with
hot or cold water. In one embodiment, a cold water wash 120 of
about 15.degree. C. to about 20.degree. C. containing from about
0.5% up to about 4% salt in solution can be used. One advantage of
salt marinade is to facilitate the primary, explosive drying step
200 when a microwave is used. Alternatively, in one embodiment, a
hot water wash 120 can help to solubilise excess starch gelatinized
by blanching a high-starch food or specific potato varieties noted
to release significant amounts of free starch (e.g. Atlantic) to
aid in subsequent processing. In an alternative embodiment the
gelatinized starch is removed by pressurized water sprays at 1.5 to
3.0 bar mounted at 25 to 50 mm above the transport belt or above
and below the transport belt to impinge on the slice surface. Both
an upper and lower belt can be used to contain the product during
transport through the high-pressure water jets, which act to de-gum
the product surface and reduce the ability of slices to adhere to
each other.
[0064] Optionally, during, prior to, or after any blanching step
110 112 114, the food slices can be marinated meaning that they are
exposed to a solution having one or more dissolved compounds to
improve the coupling efficiency of the microwave step or modify the
final product attributes. Consequently, in one embodiment, the
marinade comprises one or more ingredients selected from protective
and anti-oxidant ingredients such as sodium sulphite or bisulphate,
ascorbic acid (water soluble) or tocopherols (oil soluble); color
enhancers such as beta-carotene, and annatto; pH modifiers such as
citric or acetic acids; ionic salts such as potassium, sodium or
calcium chlorides; enzymes such as glucose oxidase, laccase,
lipase, pentosanase, transglutaminase, asparaginase, cellulase or
amylase; carbohydrate sugars such as glucose, fructose, maltose,
trehalose, and maillard reaction ingredients or long chain
carbohydrates such as carageenan, arabic or guar gums, carboxymehyl
cellulose, hydroxypropyl cellulose, native or modified starches or
protein. Because the objective of the blanching step 110 112 114 is
to deactivate enzymes rather than reduce the potato slice glucose
content, as in classic potato crisp frying, it can be beneficial
for the blanching medium to be fully saturated either by added
marinade ingredients or by the starches solubilised from the food
slice itself so that no further inherent flavor compounds are
solubilised and lost which can lead to a bland flavor in the final
crisp.
[0065] The blanching, marinade, or washing system can be configured
so that slices exit in a way that maximizes separation between
slices and minimizes overlap on the next transport section of the
process line. A speed wash, available from Heat and Control of
Haywood, Calif., USA, is an example of suitable equipment to
achieve this in a way that will improve the ease of processing in
later unit operations.
[0066] The potato slices can then optionally be dewatered 130 to
remove surface water and reduce surface tension between slices to
prevent clumping in later drying steps by contact with hot or cold
air knives for about 2 to about 3 seconds. In one embodiment, the
dewatering step reduces the free water (e.g. unbound water outside
the potato slice picked up in the washing or blanching stages) from
about 20% by weight to about 7 to about 10% by weight.
[0067] Surface moisture can be removed using an air sweep-type
dryer that employs air knives. In one embodiment, air knives
comprise heated or unheated (ambient) jets of air that are directed
above the washed potato slice while vacuum suction carries away the
dislodged moisture. In one embodiment, low pressure air (e.g. about
1.0 to about 1.4 bar) having a temperature of between about ambient
and about 120.degree. C. and a flow speed of between about 12 and
about 16 meters per second can be used for sufficient time to
remove the free surface water. In one embodiment, a multi-pass air
knife, longitudinal air tunnel, or Turbo Air Sweep as manufactured
by Heat and Control can be used. In an alternative embodiment the
slices are carried on a chain link, perforated or mesh conveyor
under and above a series of fine air knifes generated by manifolds
at 1.5 to 3 bar pressure fitted with slotted nozzles supplied by
Delevan Spray Technologies and mounted perpendicularly at 10 to 50
mm above and below the slices. A top and bottom conveyor belt
arrangement may be used to control slice agitation and achieve
effective surface water removal.
[0068] In one embodiment, the surface moisture is substantially
removed in a surface drying step 140 to prevent sticking and
clumping in later unit operations and delivers the slices evenly
distributed across a belt which is sufficiently wide and fast
enough to ensure even coverage with minimal overlap. While
monolayered slices may be considered the ideal process condition
and has been cited as a necessary arrangement step in prior art
applications (e.g. U.S. Pat. No. 5,298,707), it is important to
appreciate that monolayering is not required for this invention and
sliced food will be converted into individual finished crisps at
the end of the process. Therefore, partial overlap of at least two
slices is acceptable, which significantly simplifies the production
process, reduces footprint and improves overall economics.
Consequently, in one embodiment, transport, oiling or drying belt
coverage comprises a partial overlap of two or more slices and may
use a perforated belt constructed from metal links, which may
optionally have a non-stick coating or use a polymer belt such as
polypropylene, polyester or polytetrafluoroethylene (PTFE), which
may optionally be tessellated or perforated to further reduce
surface area contact and incidence of product adhesion to the
transport belt.
[0069] In one embodiment, for those substrates where subsequent
handling requires a very dry surface, surface water removal can be
further enhanced by routing the potato slices from air knives to an
air impingement or air jet impingement oven for between about 30 to
about 180 seconds or more preferably from about 60 to about 120
seconds in air having a temperature of between about 60.degree. C.
to about 160.degree. C. or more preferably about 120.degree. C. to
about 140.degree. C. The time/temperature combination should be
selected to dry the slice surface as fast as possible at the
highest temperature that avoids excessive gelatinization of any
surface starch. Air flows may typically range from about 1 to about
3 in/sec and should be sufficient to contact as much surface area
of all sides of the food slice as possible without excessive
lifting or displacement from the transport belt, which may cause
tearing, damage or loss of control of the food slice. If required,
a hold-down belt can be used above the food slices to control
agitation. An AIRFORCE Impingement Oven available from Heat and
Control, Inc. of Hayward, Calif., USA can be used. The objective is
to remove as much of the surface moisture as possible and to try to
achieve a surface moisture as close to about 0% as possible to
minimize surface tension effects and optimize handling
characteristics in later unit operations. This-amount of surface
moisture removal however may not be necessary for all food slice
substrates or even all potato varieties. As used herein, about 0%
surface moisture is defined such that if absorbent paper is applied
to the food slice no water is absorbed by the paper. The removal of
sufficient surface moisture has occurred when the overall moisture
content of the potato slices has reached or is lower than the
native water content e.g., the water content after slicing or prior
to a blanching step. In one embodiment, the surface drying step 140
reduces the free water from about 7% to about 10% by weight to less
than about 2% by weight and preferably to about 0% by weight.
[0070] In one embodiment, the potato slices are further dried in a
pre-drying step 150 which may utilize a microwave oven, infra-red
oven, a forced hot air oven or a combination of these may be
treated as a continuation of the surface drying step with the aim
of improving the overall cost or energy efficiencies of the drying
process. A hot air conveyor dryer, commercially available from
Aeroglide of Raleigh, N.C., USA, or a hot air rotary dryer (often
used in the food industry for rice and seeds) can be used to reduce
the moisture content by up to half of the native, raw material
starting moisture content. The lowest moisture content exiting the
pre-drying step 150 can be set as the point at which all `unbound`
moisture has been removed from the food slice. In one embodiment,
potato slices leaving the pre-drying step 150 comprise a moisture
content of between about 50% by weight and its native moisture
content (typically about 80% for a potato slice) and more
preferably between about 65% and about 75% by weight. Hot air
drying conditions should preferably be maintained at air
temperatures of about 110.degree. C. to about 140.degree. C. for
about 60 seconds to about 120 seconds. If the hot air pre-drying
step 150 reduces the average moisture content to at least 78% or
lower it can improve the mechanical strength of the slice and help
reduce excessive deformations such as folding, balling up or
clumping in subsequent explosive dehydration, if this is performed
using deep bed or rotary drying as the explosive dehydration step
200.
[0071] The improvement in mechanical strength when applying hot air
drying is thought to come from creating an `exo-skeleton` by drying
surface cells beyond their limp, low turgidity phase to create a
rigidized surface cell layer. In this way the dry surface is able
to support the body of the potato slice and mechanically resist the
tendency to fold and collapse when tumbling. Air impingement ovens
can be used to generate mechanical strength in the slice and the
higher temperature, of for example 220 C to 260 C, at impingement
air velocities reduces the processing time to around 15 to 45
seconds. However air impingement is most effective when food slices
are monolayered on a transport belt and this same hot air exposure
can degrade the finished chip texture and flavor.
[0072] Pre-drying 154 is also preferably used directly after oil
blanching 114 or after de-oiling 142. A microwave, infra-red or
forced hot air oven are suitable processing steps as described
above, however in this case pre-drying in a microwave oven 154 is
preferred as it minimizes exposure of the oil coating to hot air
which can drive oxidation. In addition, pre-drying is most easily
performed using a linear, belted oven on which the slices are
spread. The penetration of microwave energy means that a microwave
pre-dry does not require a monolayer of food slices. It is less
dependant on good spread and separation of slices than a hot air or
infra-red pre-dry where the energy must directly contact all
surfaces for efficient heating.
[0073] A significant function of pre-drying is to ensure the slice
has sufficient mechanical strength to pass through a deep bed
rotary or otherwise agitated explosive dryer 200 without creating
excessive defects to the shape or singulation of the finished
chips. Studies by others have shown that during the early stages of
drying of potato or other vegetable slices, loss of turgid pressure
in the cell walls leads to a limp slice that is incapable of
supporting itself and is more likely to stick to surfaces. A slice
at this stage of dehydration is very prone to collapsing into
undesirable shape defects, single or multiple folds, clumps and
multiple slice clusters when it encounters deformational mechanical
forces during drying. This phenomenon has been a historical barrier
to the use deep bed drying or agitated drying systems as disclosed
in this invention. Therefore, one benefit of pre-drying is to
enable the use of higher capacity, smaller footprint deep bed
processing methods where food slices are continuously agitated or
tumbled. The benefits of deep bed drying are realized since the
pre-drying step 154 is for a brief period only and can be inserted
between other deep bed equipment without the need to monolayer.
[0074] The Applicants have designed a solution using a linear
microwave pre-dryer that transports the slices on a belt to
eliminate the shape defect issue. Due to the nature of microwave
drying a moisture gradient is created within the food slice so that
the chip structure at the center of the food slice can just be set
while the outer area remains rubbery. Initiating the setting of the
chip structure creates an `endo-skeleton` at the center of the food
slice that will still allow the slice to remain elastic and adopt a
curl shape during subsequent drying steps but will prevent
undesirable shape defects or clumping due to the chip completely
folding during the rotary, agitated explosive drying step 200. A
microwave pre-dryer can fulfill this function with significant
slice overlap and without the need to monolayer since the moisture
content is only partially reduced.
[0075] Reducing the moisture content of overlapping slices too low
will result in sticking and welding of the slices to each other
creating inseparable clusters. Therefore, one benefit of pre-drying
154 is to remove a large amount of water in a way that the slices
do not weld together and will be separated in the subsequent
rotary, agitated drying step to produce singulated chips. A
microwave pre-dryer can maintain the explosive drying rates
disclosed later in this invention. Therefore this step may range
from 5 seconds to 90 seconds but is typically 5 seconds to 45
seconds in duration but preferably 10 seconds to 20 seconds in
duration, constituting a portion of the first drying phase and may
remove sufficient water to approach the first carbohydrate
transition point in the food slice as described later in this
application. It is possible the processor will remove 50% or more
of the water content of a food slice with a pre-dryer which
comprises a belt microwave where slices are allowed to touch and
overlap, however lower moistures increase the risk of product
sticking and forming clumps and increases the hazards of arcing and
consequent fires. Preferably therefore, microwave pre-drying may be
used to remove between one quarter and one half of the initial
water, for example reducing the average slice moisture content from
around 80% to around 75% wet basis (from approximately 4:1 to 3:1
dry basis) or around 80% to around 65% wet basis (from
approximately 4:1 to 2:1 dry basis).
[0076] The food slices that have not been previously oil blanched
or flash fried can then be coated with oil in an oil coating step
160 to a controlled level as required in the final product. Oil is
important to the development and finished texture, flavor and mouth
feel of the potato crisps. A thin coating of oil, preferably
applied in droplet form, can help control the number and size of
blisters that are formed when the potato slice is explosively
dehydrated' 200 in the primary dryer.
[0077] The amount of oil imparted by the coating step 160 can be
controlled to obtain desired nutritional and organoleptical
properties. Any oil or fat is suitable for the process disclosed
including vegetable oil, animal fats or synthetic oils, for example
coconut oil, corn oil, cottonseed oil, palm oil, palm olein,
linseed oil, safflower oil, high oleic safflower oil, palm stearin,
soybean oil, sunflower oil, mid or high oleic sunflower oil, rape
seed oil, lard, tallow, fish oils, olestra, sucrose polyesters,
medium chain fatty acids, diacyl glycerols, or a blend of different
oils. The choice of oil can be used to influence the final flavor
and mouth feel of the finished crisp as well as the nutrition
profile.
[0078] In one embodiment, the amount of oil added 160 is such that
the oil content of the finished dried potato slice is less than
about 10% by weight and more preferably between about 5% and about
8% by weight. In an alternative embodiment, oil is added to achieve
an oil content of less than about 25% by finished crisp weight and
more preferably about 13% to about 17% so that the finished oil
content is less than half that of regular crisps today.
[0079] In one embodiment, oil is added 160 to the potato slices by
a rotary oiler comprising spray nozzles mounted on an oil lance
placed in a rotary drum. The application rate of the oil may be
controlled by a simple drum pump and may be measured with a flow
meter if desired. For increased accuracy, the flow meter can be
calibrated to a mass weighbelt, vibro weighbelt or similar device
on the infeed or outfeed of the drum. A rotary drum design similar
to those used to season snack foods can be used. In one embodiment,
the potato slices are in a rotary oiler, 800 mm in diameter, for
between about 10 to about 30 seconds tumbling at about 10 to about
30 rpm. The rpm should be set to maintain sufficient slice
separation for coating however, the exact values will depend on the
drum dimensions selected for the quantity of slices to be oiled.
Preferably, the drum is made from a textured metal or coated with
an anti-sticking material such as polytetrafluoroethylene (PTFE) or
a fluoropolymer to minimize product sticking to the drum walls. In
one embodiment, a perforated or scored pattern can be placed along
the drum interior. In one embodiment, the drum interior comprises a
longitudinal flight to assist the tumbling action and segregation
of the food slices. A longitudinal flight or Archimedes screw can
also be used to control dwell time inside the drum. One advantage
of a rotary oiler is that the oil can be added to potato slices
without the need to monolayer and the unit can physically de-clump
any slices that may have grouped together.
[0080] In one embodiment, the coating step 160 comprises a
monolayer oil spray or alternatively a bakery oiler comprising a
spinning plate or a vertical oil curtain can be used for products
which are suited to or have been monolayered. In one embodiment,
the coating step 160 comprises marinating the potato slices in oil
at ambient temperatures or blanching or flash frying in oil at
higher temperatures as described above. In one embodiment, the
pre-drying step 150 and oil coating step 160 occurs in the same
rotary device. In one embodiment, oil addition 160 occurs during
the explosive dehydration step 200.
[0081] The addition of oil 160 to the food slice produces several
advantages. For example, oil can be used to control the formation
of blisters so that many small blisters form where otherwise large
bubble blisters may occur. This is particularly true at lower
drying rates (longer drying times) when steam is generated less
rapidly. At higher drying rates, the explosive dehydration has a
similar result by a different mechanism since a porous structure is
created by escaping steam to relieve internal pressure. Further,
oil is heated in the microwave particularly when moisture contents
are low as in phase 3 of the drying curve described later. The
heating initiates a chemical-food reaction in the oil that develops
fried flavor notes. A similar effect can be achieved if the oil is
"conditioned" by heating off line, either using conventional
heating methods, microwave energy or otherwise and then applied via
a spray onto the product. In fact, the oil can be "conditioned" by
using the oil first in other applications, such as a heating medium
for another food line. Instead of disposing the oil at the end of
its useful application as a heating medium, it can be reused as an
oil additive in Applicants' invention. When Applicants refer to
"conditioned" oil, this includes oil that has been worked
previously by any means, including, but not limited to, heat,
oxidation, and hydrolysis, if oil is applied to the product, prior
to microwaving, the oil confers the additional advantage of acting
as an energy or heat sink towards the end of the drying cycle when
the moisture content is low. This is evidenced by experiments
conducted by the inventors that reveal higher exit temperatures for
a given time or moisture content of products which have been oiled
prior to microwave drying verses non-oiled products. Consequently,
adding oil prior to the explosive dehydration step 200 reduces the
incidence of scorching in the microwave and drying can therefore
continue to lower final moisture contents without generating
undesirable burnt notes in the potato crisp or snack.
[0082] The potato slices are then routed to a microwave for the
explosive dehydration 200 step. To improve process control and
enable more accurate drying at high rates, food slices may be
routed via a mass feed weighbelt. A similar advantage is obtained
for food slices originating from doughy by forming and depositing
in pieces of controlled volume or mass. As used herein the terms,
"explosive drying," "explosive dehydration," "rapidly dehydrated"
and "primary drying" are synonymous and are defined as simulating a
dehydration profile corresponding to a fried food product that
occurs in a non-oil medium. The non-oil heating medium can include
but is not limited to, microwave radiation, infrared radiation,
radio frequency radiation, superheated steam, air and combinations
thereof. The primary energy source applied for evaporation of water
by non-oil heating may be supplemented with additional heat sources
or energy sources such as hot air, steam, superheated steam,
microwave, infrared or radio frequency radiation. Commercial
production of potato crisps typically involves a continuous process
wherein sliced potatoes are continuously introduced into a vat of
frying oil at a temperature of about 365.degree. F. (about
185.degree. C.), conveyed through the oil by paddles or other
means, and removed from the oil after about two and one-half to
three minutes of frying by an endless conveyor belt when the
moisture content of the crisps has been reduced to about 2% or less
by weight of fried chip (equivalent to around 3.0% or less of
finished chip potato weight). The resulting product generally has
texture and flavor characteristics, which are usually recognizable
by consumers as typical commercially produced continuous process
potato crisps.
[0083] FIG. 6 depicts a prior art dehydration profile of
continuously fried potato crisps 610, and is taken from FIG. 4 of
U.S. Pat. No. 5,643,626, assigned to the same assignee as the
present invention. As shown, a potato slice having a moisture
content of greater than about 80% is dehydrated to a moisture
content of about 20% about one minute and to a moisture content of
less than about 3% in about 2 minutes. Also shown by FIG. 6 is the
dehydration profile of a batch kettle fried hard bite potato crisp
having a slower dehydration profile 620 but still cooked in hot
oil. Either of these dehydration profiles 610, 620 can be simulated
in a non-oil medium in accordance with embodiments of the present
invention. By simulating these drying profiles, the present
invention can also simulate the different finished crisp textures
associated with these two dehydration profiles 610, 620 or any
profile in the spectrum of either atmospheric or vacuum frying. Not
to be limited by theory, the inventors believe that by simulating
the dehydration profile, the invention also effectively simulates
the starch conversion that occurs and is largely responsible for
the finished crisp texture. In this context `starch conversion`
refers to the temperature and moisture content of the majority of
carbohydrates in the food slice as the majority of carbohydrates
pass through each transition and the time the majority of
carbohydrates spend in each transition phase (molten/liquid,
rubbery/elastic or glass/crystalline). Carbohydrate melting and
transition points have been determined and published elsewhere
using simple capillary studies or techniques like Diffraction
Scanning Calorimetry (DSC) to measure enthalpy changes.
[0084] The present invention can be used to mimic the dehydration
profile of any fried food. Consequently, in one embodiment, the
present invention provides a method for microwave cooking a food
product to mimic the organoleptic characteristics of a fry-cooked
product. An example of how the present invention can be utilized to
provide a non-fried potato crisp having a dehydration profile that
mimics the dehydration profile of a continuously fried potato crisp
is provided below.
[0085] First, a dehydration profile corresponding to a fried food
product is identified. For example, as previously indicated, FIG. 6
depicts the dehydration profile of continuously fried potato crisps
610 and the dehydration profile of batch kettle fried hard bite
potato crisps 620. In one embodiment, the dehydration profile of a
fried food can be determined by using a continuous flume fryer and
removing samples at various distances related to certain times or a
batch catering fryer where samples are `fished` out of the oil at
certain times and moisture content then determined. Next the food
product is prepared for microwave cooking. For example, a potato
can be prepared by blanching and optional pre-drying. The potato
slices can then be cooked at a controlled power corresponding to
the power required to reproduce, mimic, or create a substantially
similar desired dehydration profile 610, 620 as depicted in FIG. 6.
This can be accomplished through trial and error by, for example,
experimenting with a belted microwave under constant power
settings, one can remove the microwaved food products at certain
times and positions to determine the related moisture contents. The
power level can be adjusted as required for the specific microwave
system and food slice combination in use. Consequently, in
accordance with one embodiment of the present invention, the
controlled power corresponding to the power required to reproduce a
dehydration profile of a fried food product comprises a first
microwave power and a second microwave power. In one embodiment,
the controlled power corresponds to transition points in the
dehydration rate of the food slice which are believed to relate to
starch transitions. The above example is provided for purposes of
illustration and not limitation. The same method described above
can be used to mimic the dehydration profile of other fried food
products including, but not limited to tortilla crisps, corn
crisps, French fries and hash browns. Since these products will
have different initial moisture contents and may optionally have
been pre-dried (e.g. in a toasting oven) the microwave drying
profile should be adapted to suit, as described above.
[0086] In one embodiment, the explosive dehydration step 200
comprises simulating a dehydration profile to a moisture content of
between about 2% and about 15% and preferably between about 4% and
about 8% by weight in an amount of time that is similar to the time
required for the comparison fried food product. The dehydration
rates and starch conversion rates in the first two phases of the
dehydration profile should be similar to and preferably match those
of the comparison fried food product to achieve similar texture.
For example, in one potato-based embodiment, the present invention
comprises dehydrating the moisture content in a plurality of potato
slices from greater than about 60% moisture by weight to less than
about 20% moisture by weight in a non-oil medium in less than about
60 seconds. In one embodiment, the explosive dehydration step 200
further comprises reducing the moisture content in the slices from
a first moisture content of between about 65% to about 80% by
weight to less than about 15% by weight in a non-oil medium in less
than about 120 seconds. In one embodiment, the explosive
dehydration step further comprises reducing the moisture content to
less than about 10% by weight or preferably less than about 2% by
weight in the explosive dehydration step in less than about 180
seconds.
[0087] FIG. 2 is a graphical representation of the moisture content
as depicted by the moisture dehydration curve 220 and temperature
profile 270 of a potato slice undergoing an explosive dehydration
step in a microwave in accordance with one embodiment of the
present invention. As shown, prior to explosive dehydration, the
potato slice comprises its native, raw state moisture content of
just over about 80% moisture by total weight 201. Of course, in
accordance with other embodiments of the present invention a
blanched and/or par-dried potato slice can comprise a lower
moisture content, as described above. Different potato varieties or
other food materials (for example carrots, parsnips, broccoli or
cauliflower) will have different raw moisture contents that may be
different than described here. At this point, 201, the potato slice
is wet, slippery, rubbery, and flexible. As the potato slice
becomes more dehydrated, it becomes drier, less slippery, but
remains rubbery and flexible 202. At this point 202 the slice is
limp and has little ability to resist folding due to a loss in
turgid pressure. Onsets of blistering begin to appear throughout
the slice, but the biggest concentration of the blistering occurs
mainly at the edges as small, flat, irregular shapes. The onset of
the blister formations can peel off implying potential steam
explosions from within the slice. No puffing is observed at this
point 202. In this approximate same time frame, the potato slice
temperature reaches the boiling point temperature 272 and there is
a relatively high rate of water vaporization 222. At the point
depicted by numeral 203, the potato slice is drier than in 202 and
there is an appearance of larger onsets of blistering throughout
the slice. Some rigidity has been restored to the slice at the
center however, the potato slice is still flexible and other areas
feel rubbery. The potato slice is not slippery at this point 203.
The temperature of the potato slice remains flat 274 for a while
after the potato slice approximately reaches the boiling point
temperature of water at atmospheric pressure. There is also a
slowing of the dehydration rate depicted by the slight flattening
224 of the moisture dehydration curve 220. Without being limited to
theory, the inventors believe that the apparent flattening 224 of
the dehydration curve coincides with the starch melting point 250
as determined in scientific literature using DSC methods, where
many of the starch solids begin to melt. In the potato slice
embodiment, the starch melting point 250 occurs when the slice has
been dehydrated to about 50% moisture by weight and when the slice
temperature is at about 100.degree. C. For ease of interpretation,
the period before this transition point has been classed as phase
1.
[0088] At point 204, the drier potato slice continues to have the
appearance of more blisters throughout the slice periphery. The
slice at this point 204 is still rubbery and flexible. At point
205, the potato slice is in the second drying phase (or phase 2)
which occurs between the two transition points 250, 260 identified
and where the starch is thought to be primarily rubber 226. The
slice at point 205 is drier than the slice at 204 and there is the
onset of a rough surface appearance and some degree of floppiness
indicating the entire slice is not yet fully set. At point 206 the
slice is hardened and appears set. Some brittleness has developed
with a certain degree of give. The surface appearance is rough
throughout.
[0089] At point 207, there is a flattening of the curve depicted by
numeral 228. Again, without being limited to theory, the inventors
believe such flattening 228 occurs as the starch enters the glass
transition stage 260 and the starch solids begin to enter into a
glassy state, labeled as phase 3. At point 208 the potato slice is
drier and more brittle than at numeral 207 and the surface
resembles a flat disk. At point 209, the potato slice is drier and
more brittle. At point 210 the slice is drier and more brittle than
at 209, and some puffed blisters are observed. At numerals 212,
213, 214, and 215 the potato slice is similar in appearance as in
numeral 211. As the potato slice moisture content is low and the
remaining moisture is less available for microwave energy to couple
with in the final glassy state 230, the temperature of the food
slice rises 280, which beneficially increases intensity of cooked
potato flavor or imparts fried flavor notes into the food slice in
the phase 3 drying stage if the slices are pre-oiled. For pre-oiled
slices during phase 3 of the drying cycle, at low moisture
contents, the microwave energy is thought to preferentially couple
with the oil. This has been observed to generate beneficial fried
flavor notes. Further, oil acts as a heat sink that helps prevent
scorching and provides a broader opportunity for moisture control
at the end of the drying process. Consequently, pre-oiled slices
make the process more controllable and products develop flavor more
characteristic of fried chips. Steam can also be used at the end of
the drying cycle to help control drying to an equal rate between
slices and avoid product scorching.
[0090] FIG. 3 is an alternative graphical representation of the
moisture content of the same potato slices depicted in FIG. 2.
Instead of the moisture content being measured on a total weight
basis, e.g. the water weight divided by the sum of the water weight
and the dry solids, the moisture content is depicted as a ratio of
the moisture remaining in the potato slice to the dry solids in the
potato slice. The actual drying rates defined by grams of water
removed per second as a ratio of the solids as depicted in FIG. 3
is a direct, primary and therefore more useful measure of the
process conditions required to achieve target textures as opposed
to a measure corresponding to the microwave power absorbed because
the power absorbed by the product is specific to the cavity and
product combination. The depiction as in FIG. 3 has been found to
be a useful assessment tool to determine and better delineate the
three different drying phases that appear to be marked by the
starch transition points. Indeed, experiments have demonstrated
that the drying rates and transition points can be defined
accurately and are highly reproducible--especially when a
homogenized food sample and/or controlled piece weight is used for
determinations. Since these drying rates have been associated with
different product textures, it is possible to precisely define the
carbohydrate transition points and the relationship between
dehydration profile and finished product attributes. It should be
pointed out that the numerals 201-215 in FIG. 2 depict the same
data, in different units, as the corresponding numerals 301-315 in
FIG. 3.
[0091] As shown in FIG. 3, the drying curve has been divided into
three distinct drying rates or phases. The first phase or first
dehydration rate 322 starts when the food slice temperature reaches
the boiling point and the moisture level begins to decrease. The
slope of the line 322 depicts the first phase dehydration rate,
which is 0.2 grams moisture per gram solid per second in the
embodiment shown. Once the potato slice reaches its starch melting
point range 350, the dehydration rate slows. Consequently, the
second dehydration rate phase 326 shown in FIG. 3 is 0.03 grams of
moisture per gram of solid per second. The second phase dehydration
rate is constant until the potato slice starch reaches the glass
transition stage 360 and passes into phase 3. In the phase 3
dehydration stage 330, the temperature of the food slice increases
to impart desired flavor notes. The exact temperature increase and
profile will depend on the level of pre-applied oil as well as
other drying energy factors.
[0092] A rise in the product temperature represents a change in
absorption of the microwave energy away from water during the
latter drying stage. Product drying can be stopped just prior to
temperatures rising rapidly toward the end of the drying cycle when
microwave energy heats organic matter of the substrate directly
rather than water. The exact temperature profile will be in part
dependent on product formulation and can be determined by trial and
error and then set as a process control parameter. Consequently, in
one embodiment, the potato slice is removed from the heating stage
330 when the potato slice reaches a certain temperature. By
removing the product before a significant temperature rise occurs,
the development of acrylamide can be minimized. In one embodiment,
the food slices are removed from the microwave at sonic time after
the slices reach a temperature of about 110.degree. C. and
preferably before reaching about 140.degree. C. and optimally
before reaching about 120.degree. C. to minimize acrylamide
formation. In one embodiment, the heating stage 330 occurs under
vacuum to further minimize acrylamide formation. In one embodiment,
the explosive dehydration step 200 occurs in a vacuum microwave.
Such an embodiment advantageously reduces the temperature of the
food slices during dehydration resulting in lowered levels of
acrylamide. Those skilled in the art will recognize that by
operating under vacuum, the temperature and moisture parameters of
the starch conversion are modified and this can be used to further
manipulate finished product texture. Therefore, in one embodiment,
all or a portion of the microwave dehydration occurs under a vacuum
where the vacuum level is selected according the finished product
texture desired. In one embodiment, the microwave comprises a micro
vacuum of between about 20 to about 80 torr where the boiling point
of water is less than about 46.degree. C. or a high vacuum of
between about 150 to about 250 torr where moisture boiling point is
between about 60.degree. C. and about 70.degree. C. In one
embodiment, the vacuum may be released or partially released
towards the end of the drying cycle to encourage flavor development
in the crisp. Alternatively, a low vacuum of about 500 to about 700
torr where moisture boiling point is between about 90.degree. C.
and about 98.degree. C. may be applied to slightly lower product
temperatures while minimizing the risk of ionizing a rarefied
atmosphere containing microwave energy. In one embodiment the
vacuum level is increased towards the end of the drying cycle to
avoid exposing heat sensitive food materials to excessive
temperature when moisture contents are low and therefore to
minimize acrylamide formation. Of course the requisite vacuum level
can depend on one or more factors including the food substrate
material, desired degree of pulling, microwave power, food
substrate shape, etc. Consequently, the vacuum can range from 0 to
about 760 torr.
[0093] It should be noted that the specific dehydration rates
depicted for three dehydration phases shown in FIG. 3 merely depict
one embodiment of the present invention. The actual drying slopes
can be controlled to simulate frying based upon the power provided
by a microwave, the design of the applicator and the composition of
the food slice.
[0094] Table 1 below depicts the dehydration rates for the three
phases for a single cavity (applicator), continuous belt, multimode
microwave run at two different power levels. Such information is
provided for purposes of illustration and not limitation. The
claims scope of the present invention applies to any microwave
system where energy is absorbed by a food slice in the microwave
field and is not limited by design specifics such as number,
location, design or orientation of waveguide inputs; microwave
frequency; number of modes; shape of cavity (applicator) etc.
[0095] The microwave heating chamber used to generate the
information depicted in Table 1 contained on average 39 potato
slices (Saturna), dry mass equivalent of about 35 grams, at any
instant. At Pf=6 ("Medium" power in this example), to achieve
drying rates of about 0.2, 0.03 and 0.004 grams moisture per gram
dry mass per second over the drying times shown in FIG. 3 required
absorbed microwave powers of about 2.6, about 0.8, and about 0.2 kW
respectively (3.5 kW in total). Therefore, the absorbed power
distribution for Phase 1, Phase 2 and Phase 3, is about 73%, about
23% and about 4% of the total absorbed power respectively.
Similarly at Pf=3 ("Low" power in this example) the drying rates of
about 0.065, about 0.01 and about 0.001 shown in FIG. 4 (discussed
below) required absorbed microwave powers of about 1.3, about 0.2,
and about 0.04 kW (about 84%, about 13% and about 4%) respectively
(1.5 kW in total). These numbers provide a guide, to one skilled in
the art, to the power distribution required in the microwave drying
process (explosive drying) in this worked example. However, these
values are specific to the pilot process (microwave cavity and
power source) in use and should be set to ensure the absorbed power
delivers the desired drying rate quoted in grams moisture per gram
dry mass per sec for which ever cavity is in use.
[0096] Since the actual energy absorbed is a function of cavity
design and product, the efficiency of a specific microwave system
must be known to set the relevant forward power. In this case,
assuming a coupling efficiency of about 70%, the Pf=6 "Medium"
power setting corresponds to power available in the cavity of 5 kW,
and the Pf=3 "Low" power setting corresponds to power available in
the cavity of 2 kW (the excess energy being absorbed by the cavity
walls and internal support structures). In both cases, reflected
power was around 1 kW, corresponding to the actual forward power
setting used in the experiments of 6 kW and 3 kW for the Pf=6 and
Pf=3 power runs respectively.
TABLE-US-00001 TABLE 1 Drying rates (grams moisture to grams dry
mass per second) Potato Slice Dehydration Rate Examples to Match
Continuous Frying of Regular PC Pf = 6 Pf = 3 (FIG. 3) (FIG. 4)
Phase 1 0.2 0.065 Phase 2 0.03 0.01 Phase 3 0.004 0.001
[0097] While not being limited by theory, the inventors recognize
that phase 1 and phase 2 appear to be responsible for mimicking the
texture generated by frying using the disclosed non-oil drying
method. Phase 1 corresponds to the evaporation of a large amount of
water. In phase 1, drying rates are highest and the inventors have
observed these drying rates are often similar between "different"
food slices (e.g. raw slices and dough slices of similar starting
moistures) for a given set of microwave conditions. This is most
likely due to the `free` nature of the moisture being removed in
this phase. Phase 2 relates to a significant starch transition
during which time the native starch is thought to be in a molten
state since this is known to occur at about 50% moisture (1 g water
per g of starch solids dry basis) at 1000. Starch melting is
traditionally slow in kettle fryers and quick in continuous fryers
so that the resultant texture varies from crunchy to crisp. Without
being limited by theory, it is possible that in phase 2, the drying
rate may be dependant on the nature of the food slice as well as
the drying energy applied since diffusion-limiting factors may be
expected to be more influential on water transport than in phase 1.
In phase 3, the starch, and therefore texture has set, so phase 3
primarily influences the finished crisp flavor and color and also
facilitates equilibration of the moisture distribution within and
between food slices.
[0098] With the knowledge that drying profiles can be divided into
three distinct phases and an understanding that these phases
influence the finished product in different ways, a drying profile
can be determined that manipulates the product texture and flavor
in a similar way to changing the profile of a fryer today from
continuous to kettle. For example, to achieve a kettle like
texture, energy input is reduced in phase 2 to simulate the slower
starch melting that occurs in kettle crisp fryers. Effectively, a
microwave can be tuned to deliver the same effects as a fryer using
energy transfer to replicate conductive heat transfer without the
use of oil.
[0099] In one embodiment, the continuous microwave cavity is
divided into multiple continuous cavities through a series of
chokes or baffles. By selecting appropriate positions for each
choke device, the microwave energy input can be independently
controlled at each point along the drying curve. This enables the
user to specify and control to different drying rates during each
phase, or if desired within a phase. Therefore, the drying rate of
phase 2 could be reduced as above tier `kettle` texture or could,
for example, he increased to match that of phase 1 in order to
reduce the overall drying time while the drying rate in phase 3
may, for example, be decreased in order to confer a broader control
window over the food slice moisture and temperature exit
conditions.
[0100] In a preferred embodiment the phase 1 and phase 2 drying
rates (R1 and R2) are controlled independently from the phase 3
drying rate (R3) by using microwave cavities that are fully
separated by means of a microwave choke. Although similar in
residence time, when simulating a fryer, the power requirements of
these two cavities are differ by the order 20:1 for R1/R2:R3.
Instrumentation to monitor temperature, moisture content and other
parameters may be used at the exit of the R1/R2 cavity and,
optionally, the R3 cavity as part of a product quality control
strategy. This situation may be further enabled by use of a product
transfer conveyor between microwave cavities or microwave and other
unit operations.
[0101] Separating the microwave drying stages conveys an advantage
to the processor's control over final chip flavor, particularly
when making controlled oil potato chips. Moisture content can be
reduced in a controlled manner to 3% to 7%, in the R3 cavity, which
significantly reduces the time required in the finish dry stage
300. Since the finish dry typically comprises hot air, this reduces
the exposure of the chip to oxidative reactions and may cut the
finish dry time from as much as 40 minutes to as little as 5
minutes.
[0102] An alternative embodiment uses batch microwave drying in
place of continuous microwave drying. Those skilled in the art will
be familiar with domestic microwaves that operate on a batch basis
with either a continuous or pulsed power input. By way of
reference, a typical domestic oven has been measured to have a
phase 1 drying rate 10 times slower than the example given for Pf=6
in table 1 above and a total drying time, approximately 4 times as
long. As outlined above, this method will deliver a harder product
texture and will create more challenging control conditions to
remove the product at an equilibrated, consistent moisture content
at the end of the drying cycle since the power input remains
constant even when moisture is low towards the end of the drying
cycle.
[0103] Therefore, in one embodiment, a batch microwave is used with
the power input adjusted over the time of the drying cycle to
simulate the energy profile of a continuous drying system. By way
of example but not limitation, for the Pf=6 example given in table
1 above, the power input (which is determined by product load and
cavity design) would be reduced at a time that coincides with the
start of each phase so that phase 1 received about 73%, phase 2
received about 23% and phase 3 received about 4% of total energy
required for drying. The power profile can be tailored to deliver
the desired product and most economic drying conditions for the
food slice taking into account that hot air addition and vapor
extraction may also be used to assist the drying process. In one
embodiment, the principle of controlling power input over time for
batch drying is applied when operating the microwave chamber under
vacuum as described above.
[0104] FIG. 4 is another graphical representation of the
dehydration rate of a plurality of potato slices in accordance with
one embodiment of the present invention. The microwave power energy
input per kg that produced the data for FIG. 4 was lower than the
power used to produce the data in FIG. 3. As shown in FIG. 4, there
are three distinct drying phases that have a high linear
correlation. The first phase dehydration rate 422 is about 0.065
grams moisture per gram solid per second. The second phase
dehydration rate 426 is about 0.01 grams moisture per gram solid
per second and the third phase 430 comprises a dehydration rate of
about 0.001 grams water per gram solid per second.
[0105] FIG. 5 is an approximate, comparative graphical
representation of the data depicted in FIG. 3 and FIG. 4. The lower
line 322a, 326a, and 330a and upper line 422a, 426a define the
drying rate window in which the target texture was reproduced for
the potato crisp product being studied. Because the lines depicting
the dehydration rates in FIG. 3 and FIG. 4 have been curve fit, the
upper and lower lines are approximate. As a result, the numerals
have the letter "a" associated to indicate the slight
variation.
[0106] As shown, the first dehydration rate 322a, second
dehydration rate 326a and third dehydration rate 330a from a
microwave oven operating at a power rate required to achieve the
depicted dehydration rates 322a, 326a form a lower boundary.
Similarly, the first dehydration rate 422a, and second dehydration
rate 426a from a microwave oven operating at a power rate to
achieve the depicted dehydration rates 422a, 426a determine an
upper boundary. It is the shaded area between these two boundaries
that corresponds to a region that mimics the dehydration profile
510 of a continuous deep-fried thinly sliced, flat cut potato
crisp. Consequently, in accordance with one embodiment of the
present invention, a food slice dehydration profile that delivers
texture and organoleptic properties similar to its fried
counterpart but occurring in a non-oil medium, lies in the shaded
region.
[0107] In summary, the study of microwave drying of food slices has
revealed three different drying phases that appear to be marked by
the starch transition point, the melting point and the glass point.
In phase 1 the drying rates are highest prior to the starch melting
and `unbound` water is substantially removed. The faster this
moisture is removed the more porous the slice surface is expected
to be and the fewer the final number of blisters. In phase 2 the
drying rates are intermediate post-starch melting and the rate at
which the food slice transitions through this phase influences how
the texture is set in the final snack. In phase 3 the drying rates
are lowest post starch glass transition. In phase 3, the flavor and
color is developed and moisture is equilibrated. Cooked potato and
fried flavor notes are imparted, particularly when oil is present
on the food slice and the oil and food slice arc heated through
microwave power coupling preferentially with the oil at lower
moisture contents and some added steam heating present during this
final moisture evaporation stage. This results in a relatively
higher exit temperature but more controllable product and process
conditions at the end of the microwave drying step.
[0108] The phase 1 and phase 2 drying rates appear to be
proportionally related when presented for continuous drying in a
uniform microwave field. Further, phase 1 appears to be product
independent while phase two appears to be product dependant. In
other words, whether the product or food slice is a dough-based
slice or a sliced raw food, such as a potato, phase 1, or the first
drying slope, will yield somewhat similar results for sliced and
dough-based foods subject to the same evaporative energy. Phase 2,
or the second drying slope, is more product dependent and the
dehydration rate will vary between sliced food and dough-based
foods. By way of example, for a raw potato slice, the phase 1 to
phase 2 slope dehydration ratio is about 6.5:1. For a potato dough
slice, the phase 1 to phase 2 dehydration slope ratio is about 3:1
in a single continuous cavity. A potato dough that has a loosely
connected cell network, caused by disrupting its native order and
therefore weakened relative to the integrity of a native slice,
will typically benefit from processing at the highest drying rates
for phase 1 to ensure explosive steam escape and minimize any
tendency to delaminate into a fragile ball or balloon into large
blisters, which can occur due to internal steam pressure at the
lower initial drying rates disclosed.
[0109] One important benefit of the present invention is that the
rate of microwave drying can influence the product texture.
Consequently, with knowledge of the carbohydrate transition points.
Which is easily determined using a belt-driven microwave cavity, a
dehydration profile can be determined that manipulates the product
texture as desired. Acceptable snack products can be made from food
slices comprising fresh raw materials in primary or explosive
drying times from about 30 seconds to over 12 minutes. Longer
drying times (specifically a longer time in phase 1 and 2) create
slightly harder and glassier textures similar to batch kettle fried
hard bite potato crisps. For example, to achieve a kettle-like
texture, energy input can be reduced in phase 2 to simulate the
slower starch melting phase that occurs in the kettle crisp fryers
today. Faster drying times (specifically a shorter time in phase 1
and 2) create more light and crisp textures similar to the fried
snack foods made in continuous fryers of today. Effectively, a
microwave can be tuned to deliver the same effects as a fryer and
can thereby replicate heat transfer without the use of oil.
[0110] A further series of experiments were performed to quantify
the preferred drying rates for each of the three phases when using
a freshly prepared potato based food slices to make snackable
foods. Potato slices in a raw slice form and were prepared using
one of the blanching methods disclosed to give a native moisture
content around 75% to 82% and a wet piece thickness of 1.4 mm. The
summary of preferred rates is given in table 2 below.
TABLE-US-00002 TABLE 2 Drying rates by phase for potato based food
slices: rates given are gram of moisture removed per second per
gram of dry matter (dry basis); ##STR00001##
[0111] In one embodiment, potato slices ranging from 1.0 mm up to
3.0 mm thick, but preferably 1.3 to 2.0 mm are processed using one
of the combinations of drying rates disclosed above. In one
embodiment potato based food slices in composite pellet form
ranging from 1.0 mm up to 3.0 mm thick, but preferably 1.3 to 2.5
mm are processed using one of the combinations of drying rates
disclosed above. As already described, each phase can be varied
independently; in a continuous or batch process, between the
maximum and minimum limits in table 2 to generate the desired
flavor, texture and appearance product attributes in the finished
food or to optimize the processing or engineering solution for the
manufacturing equipment used. Therefore, in one embodiment, any
combination of the above drying rates for each phase may be used to
process a food slice.
[0112] A method has been devised using a microwave oven to simulate
the non-oil cooking medium and accurately determine the drying
rates for each phase in order to simulate a fried food product.
This method is novel in its use of a microwave cavity to generate
data that enables starch and carbohydrate transitions to be
identified and for that information to be directly relevant and
applicable to design a process that tailors the product attributes
of a snack food to simulate its fried counterpart. While starch
transitions are known to occur in normal frying processes,
historically experimental noise associated with the methods for
determining drying profiles have masked the ability to determine
starch transitions with any accuracy. One advantage of Applicants'
method is that it does not rely on specialized or complicated
analytical equipment (e.g., Diffraction Scanning Calorimetry) to
determine the carbohydrate transition points but uses pilot or
production scale processes typical of those found in applied
manufacturing development facilities. A further advantage is that
the method is capable of sufficient precision and accuracy to
optimize product attributes and define the relevant process
conditions and to use this information to design a large-scale
production line that accurately reproduces a laboratory or pilot
product at commercial scale. Since drying rates will be influenced
by the degree of uniformity of the food product, its size, shape,
recipe and composition, it is preferable to generate initial drying
curves on a homogeneous base of the simplest geometry comprised of
the primary carbohydrate with, optionally, a controlled amount of
oil. Subsequent optimization of the process conditions can be
carried out according to the final composition and and dimensional
attributes of the product to be processed.
[0113] A single chamber, continuous conveyor microwave oven
equipped with a side-opening panel that allows full belt access
between inlet and outlet chokes is the preferred pilot experimental
equipment. A unit was designed and constructed by C-TECH,
Capenhurst, UK for this purpose. The equipment should be
temperature equilibrated at a pre-determined, fixed power before
use. Food slices are prepared and presented to the microwave oven
in a uniform configuration of rows and columns. For improved
accuracy food slices should be selected to be of similar size,
shape, weight, moisture content and moisture distribution. For
maximum piece-to-piece uniformity the food slices may be
homogenized (for example, by ricing, grinding or milling) and then
reformed into consistent pellets, optionally incorporating a
mixture of ingredients to make a composite product if desired.
Operating at fixed power the residence time of the food slices
inside the heating cavity of the microwave can be adjusted to
achieve the selected exit targets e.g. moisture content, color,
hardness or texture. When the process achieves steady state
continuous running, the conveyor belt and microwave power arc
simultaneously stopped at the point where a full food slice has
just fully entered the heating chamber. The cavity is opened and
samples are removed at each point along the belt for laboratory
moisture analysis. Each point along the belt is assigned a time
value based on the operating conditions used for the test.
Typically, six replicates of this experiment per food product per
process conditions produces sufficiently precise experimental
results. Optionally, during this experiment the temperature profile
may also be measured.
[0114] A knowledge of the temperature and moisture content of
starch or a carbohydrate can assist in predicting transition points
with reference to scientific literature or can be used to influence
and control the chemical reactions that occur in the food product
during processing. When the method disclosed is used to study
chemical reactions in food products additional functionality such
as hot air for ambient temperature control or an instant reaction
quenching method (for example, cold carbon dioxide gas) may be
added to the appropriate stage of the microwave oven chamber.
[0115] The percentage moisture loss determined over time by
laboratory analysis is converted to a dry basis rate of moisture
loss. Dry basis moisture loss makes any transitions in drying rates
more obvious. The product or process developer can then apply
linear regressions to obtain the best-fit lines and therefore
drying rates per phase. The product developer can expect to achieve
linear correlations with r.sup.2>0.8 and typically
r.sup.2>0.9 with the potential for phase 1 and 2 to approach
r.sup.2=1.0 for precisely orchestrated experiments. For a potato
based food slice dried to less than 10% moisture two transitions
and three drying phases may be determined. By way of example only,
potato starch transition points may nominally be expected at the
end of phase 1 at dry basis moisture content around 0.8 to 1.2 but
typically around 1.0 (50% water) for native potato slices and end
of phase 2 at dry basis moisture contents between 0.10 and 0.50 but
typically around 0.25 (20% water) for native potato slices. For
this method, the drying process may be considered complete at dry
basis moisture of 0.05 (around 5% water content) In this case, the
moisture content refers to the average moisture content for the
food slice noting that due to the nature of drying processes the
food slice may contain a moisture gradient.
[0116] Through iterative study or process, manipulation of these
drying phases will enable the sensory properties of a fried and
other food products to be closely simulated in order to obtain a
desired end product. Sensory properties can be evaluated using well
known consensus or blind panel techniques. Where basic cooking
parameters (moisture, time) are known, this information can be used
to reduce the number of iterations. Alternatively, if a full
dehydration curve of sufficient accuracy is known or can be
determined for the food product and process under investigation,
this can be quantified and accurately simulated by determining the
microwave power required to match the water removal rates of the
cooking system used, thus reducing iterations.
[0117] A belted or rotary microwave can be used for the explosive
dehydration step 200. A belted microwave known from frozen meat and
fish applications and available commercially from Ferrite, inc. of
Nashua, N.H., USA can be used. Belted microwaves either as single
or multiple cavities are most suited to food slices that are
molded, sheeted, extruded, stamped or otherwise deposited in an
orderly manner onto a moving belt.
[0118] Belted cavities have been presented in the prior art to
manufacture potato chips (U.S. Pat. No. 5,292,540 or U.S. Pat. No.
5,298,707) but are not generally suited to natural food slices that
are presented in a random manner, both in orientation and piece
size, as happens for example with sliced potato or other tubers. In
these cases, small piece sizes must be selected out from the
incoming or outgoing precinct stream due to improper drying and
specialized horizontal slicing that deposits slices as individual
pieces mono layered onto a moving belt must be used. The
disadvantage of this system is the relatively low belt loading that
is achieved which drives large line footprints and poor processing
efficiencies. A further disadvantage is the low throughputs that
result from avoiding large line footprints and due to the poor
capability of such slicing systems to maintain complete separation
of each slice. Without complete slice separation, a starch based
food slice is prone to ignition inside the belt microwave cavity
caused by a concentration of microwave energy and sustained arcs in
the area of close slice proximity or overlap between slices. Food
slice ignition will seriously taint the product being manufactured,
damage transport components and presents a dangerous fire hazard
for the processor.
[0119] Rotary microwaves are most suited to food slices presented
in a random manner to the explosive drying step 200 or where
product sticking is not a concern. The Applicants disclose a rotary
microwave that can receive randomly presented natural food slices,
for example potato slices from an Urschell CC slicer of the type
most commonly used on potato chip lines today, without the need to
deposit in a singular manner on a belt, to control or select piece
size or shape, manage adjacency or to separate food slices into a
single layer.
[0120] Rotary microwaves are available in other industries such as
the ceramics industry, as illustrated by U.S. Pat. No. 6.104,015
and for "microwave absorbent materials" as illustrated by U.S. Pat.
No. 5,902,510 and can he constructed for use under vacuum as
illustrated by U.S. Pat. No. 6,092,301 for tanning. Rotary
microwaves arc not promoted for use in food products but can be
used in this instance.
[0121] One advantage of using a rotary microwave is that food
slices can fold as the slices dehydrate and transition from the
rubbery state into the glassy state. As a result, the dehydrated
slices have random folds thereby mimicking the appearance of
traditionally fried snacks. Control over the formation of shape
generated by tumbling action during deep bed rotary drying of the
rood slices can be enhanced by the use of the pre-drying methods
disclosed earlier in this application. An important feature of
rotary microwave drying is that it avoids the need to partially
separate or singulate the food slices prior to explosive drying
which is a complicated operation and normally required to ensure
that randomly presented food slices do not stick together during
drying on a belt. Therefore, a further advantage to a rotary
microwave oven is that the food slices can be explosively
dehydrated in a relatively dense deep bed configuration whilst
being continuously agitated. The tumbling action maintains
individual slice separation and avoids slices sticking together
without requiring a large, uneconomic footprint that would be
needed to keep the slices separated in a monolayered or partially
mono-layered belt drying operation of typical industrial
capacities. A further advantage of rotary drying is to induce a
more familiar curled shape to the finished chip, similar to that
found in conventionally potato and corn chips.
[0122] In one embodiment, a rotary microwave that is suitable for
snack food applications is constructed in either batch or
continuous form. In its simplest form, a rotating drum that will
transport the food slices during drying is enclosed in an external
cavity. The external cavity can be built to any geometry including,
but not limited to square, triangular, pentagonal, hexagonal or
parallelogram. A circular cavity confers the opportunity to
minimize the volume of the system by accommodating a concentric
product transport drum or acting as the rotating product transport
drum itself. Food slices are fed into the cavity through a
microwave choke equipped with a transport belt or vibrating
conveyor and can be removed by similar means or by free fall
through a suitable choke.
[0123] In alternative embodiments, other novel microwave designs
may be utilized including, but not limited to, cavities that
transport slices on helical conveyors, multi-pass conveyors,
vertical trays, or accept free falling slices under gravity with or
without counter air flows. In one embodiment, steam is-added near
the end of the drying cycle when the moisture content is low to
assist in avoiding product scorching. Further, one or more
additional mediums selected from hot air, steam, superheated steam,
radio frequency, and infrared radiation can be used to assist the
explosive dehydration in the microwave.
[0124] Delivering the desired drying rates can be achieved in a
variety of different microwave applicators. Specialist applicators
such as the meander apparatus for potato chip manufacture disclosed
by Sprecher in U.S. Pat. No. 5,298,707 may achieve the target
drying rates but present significant complexity when it comes to
building a commercial scale system (typically 50 kg/hr and above).
Therefore a multimode cavity is preferred for use at commercial
scales for reasons including design simplicity, high power handling
capability and relative cost. For example, The Ferrite Company Inc.
(Nashua, USA--www.ferriteinc.com) sell bacon cooking lines based on
multimode cavities measuring 1.3 m wide, 3.7 m long and 0.8 m high,
with up to 150 kW microwave generator power at 915 MHz per cavity.
These cavities may be installed in drying trains of, for example,
six or more units.
[0125] Delivering the desired dehydration rates in food slices is
possible in other applicator types such as monomode, slotted line,
meander, fringing field, phase controlled (e.g. EP 792085), but
these cavities do not deliver economic scalability as easily or as
advantaged for snack food manufacture as with multimode.
[0126] For example, monomode applicators have width limitations
(e.g. 15 cm at 896 MHz for WR975 waveguide), require a conveyor
feed (therefore cannot tumble food slices) and the single high
intensity mode may not deliver uniform heating for foodstuffs such
as potato slices. In contrast, those skilled in the art will
appreciate that various designs can be implemented within multimode
applicators that will deliver effective and efficient drying of
food slices and that well designed multimode oven cavities can be
tailored to uniform drying of particular food slices.
[0127] Multimode oven cavities can be designed for uniformly
presented and deposited food slices even weight that are suitable
for monolayer transport through a belted cavity. Equally multimode
ovens can be designed for non-uniform, randomly presented food
slices of variable weight (for example potato slices from an
Urschell CC slicer) that are very difficult to singulate and
monolayer for uniform presentation to the microwave field. In
summary, multimode provides the greatest flexibility in designing a
process to suit the product.
[0128] In the latter case, where it is complex or inefficient to
effectively monolayer the food slices, multimode oven cavities can
be built for deep bed transport of food slices, meaning the food
slices are transported with continuous, controlled agitation in
non-continuous non-intimate contact with each other, for example in
a tumbling action. A cavity designed with this functionality
maximizes the number of slices that can be transported in a given
area which translates to higher throughput per area of plant and
will minimize food slices sticking to each other, enables steam
escape from both sides of the slice and can induce a more natural
curl appearance to the finished chip. A further benefit is the
reduced equipment footprint compared to an oven cavity that relics
on monolayer, particularly of randomly presented food slices which
causes belt loading to he particularly low to ensure no prolonged
slice to slice contact that could lead to adhesion between slices
during the drying step.
[0129] Since the rotary microwave chamber can be divided into
separate zones or independent cavities a high degree of control can
be attained on the chip exit temperature and moisture values. The
deep bed and low drying rate during the R3 period in the final
rotary microwave cavity, ensures moisture equilibration between
food slices and chips of 3% to 7% moisture can be consistently
produced, which positively benefits final flavor and texture.
Drying to lower moisture in a microwave chamber significantly
reduces the time required in the finish dry stage 300 and therefore
minimizes the risk of undesirable oxidative reactions. These are
known to occur when processors air dry for extended time periods
because it has previously been necessary to exit microwave dryers
at higher moisture contents to avoid the snack product overheating
and burning due to the limits of process design disclosed in prior
art resulting in a mismatch between product load and microwave
power.
[0130] Preferred methods to achieve deep bed transport through
tumbling action have been categorized as rotary microwaves and
include, but are not limited to, using what Applicants refer to as
Catenary Belt, Rotating Drum, and Rotating Cavity microwave ovens
designs. Each of these designs is discussed below.
[0131] A Catenary Belt design is a static multimode cavity or
enclosure with a modular polymer belt (for example intralox)
inclined a few degrees in the direction of product travel. Two
different embodiments of the Catenary Belt design are shown in
FIGS. 7 and 8. FIG. 7 is a schematic perspective representation of
a Catenary Belt microwave unit wherein the belt 702 enters the
microwave cavity (the "enclosure") at a microwave choke 706 located
at the top of the unit. FIG. 8, on the other hand, is a
cross-section view of an embodiment wherein the belt 802 enters the
microwave cavity through a choke 806 located near the bottom of the
unit.
[0132] Referring to FIG. 7, the modular belt 702 (also referred to
by Applicants to reflect this embodiment as the "Catenary Belt") is
routed over two rollers 704, at least one of which is a drive
roller which drives the modular belt 702 into the microwave cavity.
The modular belt 702 enters the microwave cavity through a
microwave choke 706. Product enters the microwave cavity by virtue
of a conveyor 710 through a microwave choke 712. Although not shown
in the drawing, product exits the unit through a similar conveyor
and microwave choke at the rear of the unit. The modular belt 702
exits the microwave cavity though another microwave choke 703
located at the top of the unit. This particular unit would also
have some type of bell cleaning apparatus, usually situated between
the two rollers 704, but is not illustrated in FIG. 7.
[0133] Referring to the cross-section view shown in FIG. 8 of a
second embodiment, again the modular belt 802 is routed over at
least two, and in this instance three, rollers 804, with at least
one of them being a drive roller. The modular belt 802 enters the
static microwave cavity or enclosure through a microwave choke 806
near the base of the unit. Product 812 can be seen tumbling on one
corner of the modular belt 802 in a deep bed configuration. This
tumbling is induced as the belt travels towards an exit microwave
choke 808. Also depicted in FIG. 8 is a belt cleaning unit 814.
[0134] The belt loci within the cavity in a Catenary Belt design
effectively simulate the quadrant of food slice contact surface
formed by a rotary drum. Modular belts are advantaged because they
can be made to form effective radii or arcs by control of the size
of their catenary sag, construction of individual belt segments,
external drive locations and feed points through the microwave
cavity. The advantage of this design is to drive the belt 702, 802
externally to the cavity and to ensure that no polymer part remains
within the cavity for more than a few seconds, which therefore
enables continuous in-line belt cleaning to remove build-up of
product debris and dielectric coatings deposited from the food
slices.
[0135] A Rotating Drum design is a static multimode cavity with a
rotating drum inclined a few degrees in the direction of product
travel enclosed therein. The drum is constructed at least in part
of microwave and vapor transparent materials to allow the food
slices therein contained to be heated directly by microwave energy
and for steam to escape. The drum can be mounted on a drive system
internal to the cavity/enclosure or can be suspended in the
cavity/enclosure and driven from outside the cavity/enclosure via
the suspension mechanism.
[0136] A Rotating Cavity design is a multimode cavity that acts to
both contain the microwave field and to transport the product. The
cavity/enclosure is mounted on an external drive system, similar to
rotary hot air dryers known within industry, and the whole
cavity/enclosure is rotated between static end plates. Thus, this
embodiment comprises a rotating enclosure, as opposed to the static
enclosures of the two previous design examples.
[0137] FIG. 9 is an illustration of a two-cavity embodiment of the
Rotating Cavity microwave unit. This unit comprises a first
cavity/enclosure 902 and a second cavity/enclosure 904 that both
rotate on, and are driven by drive wheels 906 that are external to
each of the cavities 902, 904. One or more wave guide feeds 916, at
different orientations, can be used to control cross-talk between
microwave signals. One or more microwave feeds 918 can penetrate
into the cavity as well, to allow more controlled delivery of
microwave energy. In a preferred embodiment, a duct 922
communicates with the cavities in order to facilitate hot air feed
and/or steam extraction. This duct 922, in a preferred embodiment,
is a polymer sleeve insert. At least one separate wave guide feed
920 provides microwave energy specific to the second cylinder 904.
In one embodiment, the two rotating microwave cavities are separate
and joined only be a product transport conveyor to ensure complete
control over the microwave power levels applied to each chamber. An
end-feed conveyor 910 routed through a microwave choke 922 is used
to introduce product into the first cavity. As the cylinders 902,
904 rotate and tumble the product within the cavity, a slight
incline on the entire unit causes a gravity feed of the product
from the first cylinder 902 into the second cylinder 904. Product
is then removed from the second cylinder 904 by another conveyor
914 that also passes through a microwave choke 924. In one
embodiment the microwave choke and product release at the exit of
the chamber is accomplished by the use of a rotating valve with
several pockets.
[0138] Each design (Catenary Belt, Rotating Drum, and Rotating
Cavity) benefits from longitudinal flights to lift and tumble the
product slices on the walls of the drum, cavity or belt. While this
is sufficient to control the tumbling action and transport of the
food slices, additional features may also be added, for example an
internal helix of fixed or variable pitch in a rotating cavity or
drum can improve control of residence time. Any of the designs may
be configured as singlezone or multizone drying trains and the
drying efficiency of any of the microwave ovens may be assisted by
hot air, steam, superheated steam, infrared or other methods of
heat and energy transfer.
[0139] Each design has different advantages and challenges when
considered for commercial production. Static cavities, such as is
found in the Catenary Belt embodiment and the Rotating Drum
embodiment, allow power feed locations to be selected over a very
large area of the cavity and preferred feed arrangements are well
known in the art. This is important for large-scale installations
that may draw 1 MW or more per cavity. Rotary cavities restrict the
area available for microwave power inputs. The static end plates
provide the greatest area but present additional design complexity,
for example: avoidance of cross-coupling of microwave fields
between multiple feeds in close proximity, mechanical design to
allow the static end plate to act as a door to allow personnel
access to the cavity for cleaning, maintenance etc.
[0140] On the other hand, a Rotating Drum stays within a static
cavity during processing and will be subjected to high temperatures
(typically 100.degree. C. and over) from contact with the hot food
slices, steam generated by the food slices, and possibly externally
applied hot air and/or steam to aid the drying process.
Additionally the drum can become coated with dielectric materials
(for example oil, starch, sugar, salt etc.) picked up from contact
with the food slice. The drum is made at least in part from
microwave transparent components for which polymer is typically
used for reasons including mechanical performance, microwave
transparency, cost and ability to be machined to desired form. When
polymer inside a microwave field becomes coated with dielectric
materials, there is a significant risk that the coating will
self-heat leading to damage or melting of the polymer, which is
more likely with the high microwave power densities required to
achieve the initial drying rates disclosed herein than in
conventional microwave drying processes such as bacon drying. To
minimize the risk of damage to polymer parts within the microwave
cavity, the polymer must be thoroughly cleaned on timescales
typically more frequent than traditional food production cleaning
schedules would ideally allow (for example daily rather than weekly
in snacks manufacture). One way to improve this situation is to use
a Catenary Belt running through a static cavity, which enables a
polymer transport construction to he used in the microwave field
while also providing the opportunity for continuous cleaning, which
considerably reduces the risk of damage to the polymer.
[0141] A Rotating Cavity overcomes the disadvantages of having to
use microwave transparent materials or polymers inside the
microwave oven cavity and eliminates any complex internal
architecture that may be needed to support, drive or remove drums
or belts for cleaning and maintenance. While it is possible to
construct a rotating cavity with polymer linings to minimize or
fully eliminate sticking of food slices to the cavity walls and
those linings can have surface finishes applied to reduce effective
surface contact area, the preferred embodiment of the rotating
cavity design uses the metal walls to tumble slices and therefore
eliminates maintenance and cleaning issues associated with polymer.
The effective contact surface area between wall and food slice can
he reduced using textured finishes such as dimples or grooves, or
applying holes or slots in the food slice contact metal surface
itself in order to make the metal surface of the rotary drum less
sticky to food slices. A suitable Rotating Cavity material is
stainless steel 6WL provided by RIMEX, although other microwave
reflective materials may be used including but not limited to
metals such as Aluminum. The preferred embodiment is for such
surface to comprise a non-stick metal surface. The food slices are
tumbled in the microwave field by the rotating action of the
cavity. The cavity can be rotated using drives external to the
microwave field.
[0142] A disadvantage of rotary cavities is the complexity of the
rotary jointed choke that is required between the rotating cylinder
and static end plates. Static end plates are preferred to
facilitate ingress and egress of hood slices on linear conveyors,
microwave power via rigid waveguides and hot air and/or steam via
conventional pipe work.
[0143] As shown in FIG. 9, multiple cavities may be placed in
series to create a multizone dryer as described earlier in relation
to the 3 phase drying curve. It should be understood that a
multizone dryer can be created from both multiple rotating
cavities, and multiple static cavities, or a combination thereof or
by combining linear, belted cavities with a rotary form. One cavity
may be used for a selected part of the drying curve only, for
example half of phase one phase one only, or phase one and two
together. In one embodiment, multiple cavities may be used for the
first phase where power requirements are highest. Advantages have
already been cited for multizone configurations using more than one
microwave cavity, including improved control of power distribution,
power tuning and consistency of final product since the microwave
cavity can he sized to the intended product loading, dielectric
properties or other drying characteristics. It will be appreciated
by those skilled in the art that there are many approaches to
construct multiple multimode cavities, for example, by baffling or
otherwise partitioning is large single multimode cavity into two or
more zones. The degree of isolation required between baffled zones
within a single multimode cavity or multiple rotating multimode
cavities (which are linked by rotary jointed chokes and not
internally choked) or combinations thereof may be high (e.g. 20 dB
or more) to generate the drying rates required to achieve the
preferred product attributes, or low (e.g. around 10 dB) if a
single drying rate zone is split up into multiple cavities to
assist power delivery. Alternatively, the static and/or rotary
single or multiple multimode cavity(s) may be used without
isolation such that the selected drying conditions (e.g., water
removal rate, moisture content entering and exiting microwave
cavity) determine the preferred drying curve.
[0144] Baffling may be preferred where multiple static cavities arc
used in order to minimize product transfer distances through full
chokes, which may occur at critical points in the drying curve.
While baffles can be inserted between sections of rotating drums or
rotating cavities, rotating cavities with no other microwave
containment also require a rotary choke between rotary chambers.
Such rotary jointed chokes are well known, for example in radar
applications, but are novel in this application since they have not
been used for rotary cavities of diameters up to around 3 m that
are suitable for handling commercial scale snack production
volumes. A notable advantage of rotary chokes is the avoidance of
large transfer zones, which may for example occur through discharge
chokes, outlet conveyors and inlet conveyors between static
multimode cavities. Such transfers can create opportunities for
food slices to be inadvertently held up in the microwave field. The
rotary choke itself may only be a few centimeters wide and the
product flow across the choke acts to clear slices should any
become held up.
[0145] An important design consideration for tumbling of food
slices (whether by drum, rotating cavity or modular belt) is the
balance between inertial and gravitational forces to achieve
sufficient non-intimate contact with minimal physical damage.
Trivial cases are when rotational speeds arc too high, food slices
will stick to the contact surface through centrifugal forces; if
the rotational speed is too low, food slices will slide against the
contact surface. Suitable conditions for delivery of preferred
product attributes depend largely on drum diameter (or effective
diameter if the modular belt design previously described is used)
and rpm. Additionally, use of longitudinal flights, weirs, spirals
or other devices which assist the tumbling action of the food
slices have a significant impact on delivery of preferred product
attributes. One useful approach to maintain optimum tumbling
conditions (during scale-up or when using multiple rotating
cavities of different diameters) is use of rpm, circumferential
speed and the Froude number. The Froude number (Fr) is a
non-dimensional scale-up parameter defined as N.sup.2 D/g for
rotating drums, where N is drum rpm, D is the diameter (m) and g is
gravity (m/s).
[0146] Referring back to FIG. 1, after the explosive dehydration
step 200, the slices can be finish dried 300 to a moisture content
of less than about 3% by weight of potato solids in the finished
chip. A hot air dryer having a belt configuration operating at
about 80.degree. C. to about 140.degree. C. or other suitable
methods can be used alone or in combination. Other suitable finish
drying 300 methods include one or more drying methods selected from
hot air, infrared, radio frequency, and microwave. The slices can
optionally be salted or seasoned 400 by methods well known in the
art. An oil spray step can be used after the finish dry step 300
either before or in conjunction with the seasoning step 400 to
tailor the final oil content and assist with seasoning
adhesion.
[0147] The above unit operation examples arc provided by way of
illustration and not by way of limitation. Further, those skilled
in the art will appreciate that many of the processes discussed
with the potato slice embodiment above can be used with other food
slices, including, but not limited to, beets, beans, carrots,
bananas, apples, strawberries, lentils, wheat, rice, parsnips,
Jerusalem artichokes, potatoes, noble nuts, peanuts and coated
peanuts, masa, and corn. Starchy tubers are especially preferred.
Further, those skilled in the art will recognize that if processing
steps are applied to other raw foods besides potatoes, such foods
may require processing times and temperatures different than those
disclosed. However, such embodiments are intended to be covered by
the claims scope of the present invention.
[0148] Doughs, in accordance with the present invention, can
comprise entirely fresh raw materials or a mixture of fresh and
dried raw materials such as native or modified starches.
[0149] Additional ingredients including, but not limited to,
seasoning, oil, nuts, seeds, pulses, and other inclusions such as
fresh or dried herbs and spices may also be added to a dough. One
advantage of the invention is that relatively fragile dough, for
example with high moisture contents over 65%, that may not be
sufficiently cohesive for frying can be processed and dried using
the continuous belt microwave or batch microwave embodiments of
this invention. A suitable dough may be prepared using familiar
kitchen methods and domestic practice. For example, optionally
peeling and then chopping potatoes ready for steam cooking on a
stovetop. Once softened, a hand masher can be used to make the
dough and optionally incorporate culinary ingredients, for example
olive oil, salt and pepper. A rolling pin can be used to form a
thin sheet of around 3 mm from the dough from which shapes can be
cut with a pastry cutter. Shapes can be lifted and placed into the
non-oil drying apparatus using a spatula. While domestic non-oil,
drying or baking methods are suitable for finishing this product,
those skilled in the art should understand that the preferred
drying rates disclosed arc a requirement for optimal snack product
quality and are typically out of the achievable range of domestic
microwaves and other non-oil drying equipment.
[0150] Commercial scale processing solutions to cook fresh
materials in preparation for making a sheet or dough are known from
the prior art and current industrial practice in, for example, the
potato flaking industry. Typically this involves size reduction,
for example by chopping potatoes in half or dicing into slabs,
followed by steam cooking. Amongst others, Lyco manufacture a range
of rotary drum blanchers. BMA and ABCO supply steam based heat and
hold systems capable of cooking either potato or vegetable
material. Cooking times are well established by equipment
fabricators and vary according to piece size but are typically of
the order of 10 minutes at around 90 C. The frozen potato and
potato specialty industries utilize equipment such as Alimetee's
Hoegger Separator to make smooth dough from materials cooked in
this manner. Conventional snacks food slice preparation equipment,
for example a masa sheeter and cutter, can be used to form and
deposit shapes from the dough. Alternatively, the principles taught
by U.S. Pat. No. 4,212,609, whereby a uniform air pressure ejects
food material from a porous mould on a rotating drum, can be
adapted to the food slice forming for this invention.
[0151] In a preferred embodiment a uniquely shallow mould of around
1 mm to 4 mm depth is designed specifically for food slice forming
and deposition onto a moving belt. The shape of an individual mould
may vary in comparison to adjacent moulds in order to produce
different shapes, for example by changing the circumferences or
planes of the mould. Therefore, one important benefit that improves
the natural appearance of the chip is the ability to deposit free
form shapes without the need for tessellation of the shapes, which
requires straight edges to the chip, or recirculation or the dough
as required with current commercial snack forming methods. In
addition, multiple shapes may be deposited from the same machine
almost simultaneously.
[0152] Recently, Stork Food Systems have introduced their Revo
Former (patent application WO 2004/002229), which operates on the
principle of forming various food patties from meat, fish or potato
in rotating porous moulds and then expelling the food patties with
uniformly distributed forced, air. This equipment offers an
alternative to conventional food slice sheeting systems, for
example masa sheeters used in the production of corn chips, since
the moulds of the Revo Former can be adapted to form and deposit
thin food slices in different shapes in an efficient, high speed
and hygienic manner suitable for use at commercial production rates
in this invention. In addition, because the food slices are
uniquely expelled from a mould and do not need to be cut from the
dough, this forming method is able to handle composite recipes,
which may contain fibrous or stringy ingredients that would
typically contaminate a traditional snacks forming operation.
[0153] By way of example, the food slices may be 1 mm up to 4 mm
thickness, but preferably 1.5 mm to 3.0 mm, and comprise entirely
fresh dough made from corn, potato or a composite recipe of, for
example, potato and vegetable or pulses. One advantage of this
forming system is to shape and deposit dough made from fresh
ingredients, where the dough may be fragile, sticky or deform under
its own weight due to the high native moisture content. Moisture
contents may be 65% or greater on a wet basis, for example 78% to
82% for a potato based dough. Therefore, in a departure from prior
art, for example United States Patent Publication 2006/0188639 or
United States Patent Publication 2005/0202142, the processing
method disclosed is not dependant on preparing dough with specific
properties for snacks manufacturing and can form and dry food
slices from doughs comprising 100% fresh, non-artificial materials,
without the need to fragment and recombine as a laminate or
cluster. Furthermore, the non-fried method disclosed can
manufacture snack chips at commercial line throughputs comparable
to large snacks manufacturing lines today starting from fresh, high
moisture raw materials and without the need to use dried
ingredients to reduce the moisture load or to use frying as a
highly efficient method of drying high moisture raw food
materials.
[0154] Depositing food slices in a uniform manner onto a moving
belt, which enters an explosive drying step, is an efficient method
of enabling the use of high intensity, explosive microwave drying
at commercial throughputs. As discussed previously, randomly
presented food slices, for example from an Ursheell CC slicer,
result in poor efficiency in both throughput and footprint occupied
by the explosive drying step since, to minimize fire risk and avoid
product pieces welding together, it is necessary to maintain
separation between food slices, which in turn reduces the energy
transfer efficiency during explosive microwave drying.
[0155] When the processor wishes to incorporate oil or an optional
medley of other ingredients to enhance the flavor experience or
nutritional benefit of the food slice a simple mixing step can be
included prior to forming. The Hobart Legacy is one example of a
suitable mixer of the bowl and beater paddle type commonly used in
the bakery industry. However many industrial solutions to mixing on
a batch or continuous basis are readily available according to the
number and type of the ingredients in use and the processor must
account for the preferred preparation method of each ingredient,
for example grating, grinding, fine chopping or shredding and
important food manufacturing standards, for example hygiene,
associated with processing high moisture dough.
[0156] In a preferred embodiment of this invention, a food slice
prepared in this way will be transferred directly to a belt
microwave for explosive drying. No other treatment or preparation
steps are necessary using the disclosures of this invention.
Several suitable belt types, made from for example polypropylene,
polyethylene or PTFE coated fiberglass, are available from
microwave oven manufacturers to transport the food slices in this
application.
[0157] In one embodiment, the fresh dough slice is rapidly dried to
a moisture content around 15% to 25%, close to the final glass
transition point, in under 90 seconds. In a preferred embodiment
the dough slice is dried to the same moisture level in 15 seconds
to 60 seconds and more preferably the food slice is dried to
moisture content at or below 25% in 25 seconds to 35 seconds. At
this stage, drying may continue in the microwave chamber to a
moisture content between 18% to 5%. The exit moisture will in part
depend on the ingredients of the composite food slice being
processed. In a preferred embodiment, food slices that continue to
be dried by microwave cooking arc transferred to a separate zone in
the microwave chamber or to a separate microwave cavity when the
moisture content is around 25%. A. separate microwave cavity may be
of the linear belted forum or rotary form. The power is then
independently controlled to reduce moisture content o somewhere in
the range of 3% to 15% but preferably in the range of 5% to 8%
before entering a conventional hot air oven to reach their final
shelf stable, snackable moisture content around 2%.
[0158] In an alternative embodiment drying from around 25% moisture
to 2% is completed in hot air, multizone oven as for conventional
snack foods. In one embodiment, slices are final dried in a hot air
oven at between 110 C to 130 C until shelf stable moisture of
around 1% to 2% is achieved. As discussed earlier, the initial
rapid drying is a unique method for simulating the fried texture
of, for example potato chips, for non-fried food slices made from
fresh ingredients and the subsequent slower drying at lower
moisture contents ensures desirable flavor development. The exact
choice of temperature and process conditions for the final drying
stages will largely depend on the food slice recipe in use and the
level of temperature sensitive food chemistry reactions, for
example maillard browning, that occur due to the ingredients
present. In one embodiment, composite food slices formed from a
fresh dough into 1 mm to 4 mm, but preferably 1.5 mm to 3.0 mm deep
pieces with a moisture content of 65% to 85% but preferably 70% to
80% are dried according to the rates disclosed below.
TABLE-US-00003 TABLE 3 Drying Rates by phase for potato based food
slices formed from dough: rates given are gram of moisture removed
per gram of dry matter (dry basis) Preferred Minimum Range Maximum
Phase 1 0.04 0.06-0.18 0.20 Phase 2 0.01 0.03-0.06 0.08 Phase 3
0.0005 0.002-0.02 0.03
[0159] As discussed earlier, Phase 2 represents a significant
carbohydrate transition, which occurs from around 50% average
moisture content to around 25% average moisture content and is
thought to be related to starch melting in a potato based food
slice. For a potato slice with the Applicants' preferred texture,
the Phase 2 period is between about 5 seconds and about 50 seconds
or preferably between about 10 seconds and about 30 seconds.
[0160] Those skilled in the art will appreciate that the drying
times disclosed are extremely rapid compared to conventional
non-frying technologies. Therefore, a fundamental advantage of this
invention versus other heating methods is high capacity
manufacturing of non-fried snacks. Thus, this invention overcomes
the limitations on profitable, commercial manufacture of non-fried
snacks. This limiting barrier occurs due to the fresh starting
material that, while conveying benefits to the finished consumer
product, requires large volumes of water to be removed. The
limiting barrier is particularly increased due to the light piece
weight of food slices that arc suitable for snacking, especially
when in the form of a chip that yields low product weight per area
of transport belt. The limiting barrier is further increased when
the light weight food slice comprises a dough where the properties
are such that individual pieces must maintain their singulation,
for example in a mono layered bakery line configuration, to avoid
sticking, clumping or other shape defects. Thus, in an unfavorable
difference compared to sweet or bread baking lines, a non-fried
snacks line that produces thin, bite size pieces where the weight
of 10 dried pieces may range from just 7 g to 15 g or preferably 8
g to 12 g, will have to dry product at low piece density, for
example, 1 kilogram per square meter of wet food slices. These
limitations, particularly in combination, drive large dimensions,
energy inefficient and low throughput snack manufacturing lines
when utilizing prior art or conventional non-fried drying
technology. Therefore, this invention conveys to the user
associated commercial benefits of footprint and line layouts that
are comparable to conventional fried snack food manufacturing lines
today.
[0161] By way of example, and by no means limitation, exciting
recipes-suitable for the food slices described and that can be
processed into consumer-optimised snacks with crisp-like texture by
drying to approximately 2% moisture are:
[0162] Example 1 (by wet dough mix weight): 85% potato, 12%
legumes, for example chickpea, 3% oil, 0.1% coriander leaf, 0.1%
whole cumin; which is equivalent to a finished chip of 72% potato,
16% chickpea, 11% oil, 0.5% coriander leaf, 0.5% cumin by
weight;
[0163] Example 2 (by wet dough mix weight): 49% potato, 46%
lentils, for example Chuna Dhal lentils, 4% oil, 1% herbs and
spices to season, for example selected from chili, garlic, cumin or
turmeric; which is equivalent to a finished chip weight of 33%
potato, 53% lentil, 13% oil, 1% herbs and spices.
[0164] Example 3 (by wet dough mix weight): 70% potato, 25% mixed
root vegetables selected from, for example, carrot, parsnip .and
swede, 3% oil, 1.5% onions and 0.5% mixture of pepper and herbs,
for example selected from thyme, rosemary or tarragon to season;
which is equivalent to a finished chip weight of 67% potato, 13%
root vegetables, 16% oil, 3% onion, and 0.5% mixture of black
pepper and herbs.
[0165] Example 4: 70% potato. 25% cauliflower or other brassica, 3%
oil, 1.5% onions, 0.2% ginger, 0.2% garlic; 0.1% turmeric; which is
equivalent to a finished chip weight of 67% potato; 13%
cauliflower, 16% oil, 3% onion, 0.5% ginger, 0.4% garlic and 0.1%
turmeric.
[0166] In one preferred embodiment, the potatoes used for the food
slice dough contain a starch solids content of 21% or higher.
[0167] There several product advantages provided by the present
invention when used with dough based food slices. First, the
process allows the nutritional profile of the product to be
controlled. For example, oil is added in controlled amounts either
before and/or after the primary drying step. One advantage of
adding oil before the explosive dehydration is that it will be
heated for a short period toward the end of the explosive drying
and this develops desirable fried-flavor characteristics that are
not developed with conventional baking or impingement ovens.
Another advantage provided by the present invention is the
processing temperatures. Because the processing temperatures are
relatively low throughout the food slice (e.g. can be maintained at
about 100.degree. C. even on the outer skin) when compared to
conventional hot oil frying, and the processing times are
relatively short, e.g. less than about 60 seconds is achievable
even for high moisture doughs, less of the inherent nutrition is
expected to be destroyed during the drying process and natural
flavor characteristics of the substrate or added ingredients
derived from nuts, seeds, pulses, herbs, spices etc. are retained.
Similarly, nutritionally desirable vitamins, essential fatty acids
or phytonutrients inherent in the added ingredients or directly
added for fortification are expected to be retained. Further, the
low temperature and short drying time benefits the use of natural
ingredients if added as flavorings or seasonings in dough-based
embodiments.
[0168] By definition, natural ingredients have originated from
nature without undue processing and occur in forms that are readily
recognizable as the original ingredient through, for example
appearance, color, flavor or texture even after preparation for
storage, which may include washing, blanching, smoking, dicing,
freezing or storage in oil as examples. Natural ingredients can be
incorporated into a food slice dough, to be visible and
recognizable in the snack foods manufactured with the Applicants'
disclosure, but arc not typically suitable for topical coating of
snacks foods due to their relatively large size and irregular
shape. By contrast, ingredients that have been processed or
homogenized in form, for example powder, granulated or flaked and
are a longer recognizable from the original starting material would
be considered artificial and are typically used in topical coatings
today.
[0169] When incorporated into food slice recipes natural
ingredients substantially retain their fresh appearance due to the
relatively low drying temperatures of this invention. By way of
example only, fresh mint or coriander leaf in the dough will appear
much more fresh, green and whole than when processed by a hot air
oven which causes a degradation to appearance since the leaf
becomes dark green and shriveled by the heat. This drying method
and profile also helps to ensure that any natural ingredients added
can deliver an authentic, vibrant flavor to a finished product
because the natural ingredients added for reasons of flavor,
texture or fortification, can be expected to retain a significant
portion of their inherent nutritional and organoleptic value
without losing desirable aroma, flavor, color or phytonutrient
compounds. Consequently, a significant advantage be dough based
food slices illustrated is to produce a snack where the flavor is
derived entirely from the natural ingredients, for example
vegetables, herbs and spices, in the dough base. In this case, the
snack does not require topical, powder seasoning that is typically
used on snack foods today. Therefore, the snack does not require
powder, flake, granule or any artificial ingredient to be
incorporated in the dough of the food slice or as a coating to the
snack chip to deliver a consumer optimized flavor. The absence of
topical powders ensures the snack is substantially clean on the
fingers when eaten, thus avoiding a common consumer complaint of
conventional snack foods. Furthermore, one important benefit of the
ability to make snack foods using natural ingredients is the
relatively low sodium level required for a consumer-optimized
flavor. Typically, topically applied salt can be reduced to 50% of
the level of potato crisps today or eliminated from the recipe
while still delivering a palatable consumer optimized snack
flavor.
[0170] In addition, the present invention provides a way to provide
a balanced nutritional profile using real thud ingredients, such as
vegetables, nuts, seeds, herbs, and spices or cheese. Vegetables
that can be used include, but are not limited to carrots, parsnip,
sweet potato, turnip, squash, courgette, asparagus, mushroom,
broccoli, cauliflower, sweet pepper, chili pepper, peas, sweetcorn,
celeriac, tomato, olives, aubergine, beetroot, fennel, onions,
spinach, chard and cabbage. Nuts that can be used include, but are
not limited to almonds, peanuts, walnuts, pecans, and brazils.
Seeds that can be used include, but arc not limited to pumpkin,
sunflower, sesame, poppy, and squash. Pulses and legumes that can
be used include but are not limited to peas, chickpeas, lentils,
pinto beans, kidney beans, broad beans, butter beans, soy beans,
runner beans or black eye beans. Cereals that can be used include
but are not limited to oats, wheat, sorghum, rice, millet, rye, and
barley. Herbs and spices that can be used include but arc not
limited to basil, bay leaves, coriander, mint, cumin, garlic,
lemongrass, oregano, paprika, turmeric, parsley, and pepper, just
to name a few. Natural oil extracts can also be used either prior
to or post primary drying.
[0171] Advantageously, because the real food ingredients can be
added after any blanching step, and because of the relatively lower
temperatures and short dwell time during dehydration, the flavor
profiles are more pronounced than prior art snacks that are cooked
in high temperature ovens or fryers. Further, because there is no
oil or water medium, the nutrient content and flavor profiles do
not leach out. Consequently, unlike the prior art, the present
invention provides a way to formulate natural flavor profiles
without the use of artificial ingredients.
[0172] While the invention has been particularly shown and
described with reference to a preferred embodiment, it will be
understood by those skilled in the art that various changes and
form of detail may be made therein without departing from the
spirit and scope of the invention.
* * * * *